• Skip to main content
  • Skip to search
  • Skip to select language
MDN Web Docs
  • References
    • Overview / Web Technology

      Web technology reference for developers

    • HTML

      Structure of content on the web

    • CSS

      Code used to describe document style

    • JavaScript

      General-purpose scripting language

    • HTTP

      Protocol for transmitting web resources

    • Web APIs

      Interfaces for building web applications

    • Web Extensions

      Developing extensions for web browsers

    • Accessibility

      Build web projects usable for all

    • Web Technology

      Web technology reference for developers

  • Learn
    • Overview / MDN Learning Area

      Learn web development

    • MDN Learning Area

      Learn web development

    • HTML

      Learn to structure web content with HTML

    • CSS

      Learn to style content using CSS

    • JavaScript

      Learn to run scripts in the browser

    • Accessibility

      Learn to make the web accessible to all

  • Plus
    • Overview

      A customized MDN experience

    • AI Help

      Get real-time assistance and support

    • Updates

      All browser compatibility updates at a glance

    • Documentation

      Learn how to use MDN Plus

    • FAQ

      Frequently asked questions about MDN Plus

  • Curriculum New
  • Blog
    • Playground

      Write, test and share your code

    • HTTP Observatory

      Scan a website for free

    • AI Help

      Get real-time assistance and support

  • Log in
  • Sign up for free
  1. Glossário do MDN Web Docs
  2. undefined
    • English (US)
    • Deutsch
    • Español
    • Français
    • 日本語
    • 한국어
    • Русский
    • 中文 (简体)

Esta página foi traduzida do inglês pela comunidade. Saiba mais e junte-se à comunidade MDN Web Docs.

Neste artigo

  • Aprenda mais
  1. Glossary
    1. Abstração
    2. accent
    3. Acessibilidade
    4. Árvore de Acessibilidade
    5. Accessible description
    6. Accessible name
    7. Adobe Flash
    8. Advance measure
    9. AJAX
    10. Algoritmo
    11. Contêiner de Alinhamento
    12. Tópico de Alinhamento
    13. Alpha (canal alfa)
    14. ALPN
    15. API
    16. Apple Safari
    17. Application Context
    18. Argumento
    19. ARIA
    20. ARPA
    21. Arpanet
    22. Array
    23. ASCII
    24. Aspect ratio
    25. Assíncrono
    26. ATAG
    27. Atributo HTML
    28. Authentication
    29. Authenticator
    30. Bandwidth
    31. Base64
    32. Baseline
      1. Baseline (compatibility)
      2. Baseline (typography)
    33. Beacon
    34. Bézier curve
    35. bfcache
    36. BiDi
    37. BigInt
    38. Binding
    39. Bitwise flags
    40. Blink
    41. blink element (<blink> tag)
    42. Block
      1. Bloco (CSS)
      2. Block (scripting)
    43. Block cipher mode of operation
    44. Elementos block-level
    45. Booleano
      1. Boolean (JavaScript)
      2. Boolean attribute (ARIA)
      3. Boolean attribute (HTML)
    46. Bounding Box
    47. Breadcrumb
    48. Brotli compression
    49. Navegador
    50. Browsing context
    51. Buffer
    52. Bun
    53. Cache
    54. Cacheable
    55. CalDAV
    56. Call stack (Pilha de chamadas)
    57. Função Callback
    58. Camel case
    59. Canonical order
    60. Canvas
    61. Card sorting
    62. CardDAV
    63. caret
    64. CDN
    65. Certificate authority
    66. Certified
    67. Challenge-response authentication
    68. Caractere
    69. Character encoding
    70. Character reference
    71. Character set
    72. Chrome
    73. CIA
    74. Cipher
    75. Cipher suite
    76. Ciphertext
    77. Class
    78. Client-side rendering (CSR)
    79. Closure
    80. Cloud
    81. Cloud computing
    82. CMS
    83. Code point
    84. Code splitting
    85. Code unit
    86. Codec
    87. Color space
    88. Color wheel
    89. Compile
    90. Compile time
    91. Composite operation
    92. Compression Dictionary Transport
    93. Programação de Computadores
    94. Conditional
    95. Constant
    96. Constructor
    97. Content header
    98. Continuous Media
    99. Control flow
    100. Cookie
    101. Copyleft
    102. CORS
    103. CORS-safelisted request header
    104. CORS-safelisted response header
    105. Crawler
    106. Credential
    107. CRLF
    108. Cross Axis
    109. Cross-site scripting (XSS)
    110. CRUD
    111. Cryptanalysis
    112. Cryptography
    113. CSP
    114. CSRF
    115. CSS
    116. Modelo de Objeto CSS (CSSOM)
    117. Pixel CSS
    118. Pré-processador CSS
    119. Cumulative Layout Shift (CLS)
    120. Data structure
    121. Database
    122. Debounce
    123. Decryption
    124. Deep copy
    125. Delta
    126. Denial of Service (DoS)
    127. Deno
    128. Descriptor (CSS)
    129. Deserialization
    130. Developer Tools
    131. Device pixel
    132. Digital certificate
    133. Digital signature
    134. Distributed Denial of Service (DDoS)
    135. DMZ
    136. DNS
    137. Doctype
    138. Document directive
    139. Document environment
    140. DOM
    141. Domínio
    142. Nome de domínio
    143. Domain sharding
    144. Dominator
    145. DSL
      1. DSL (Digital Subscriber Line)
      2. DSL (Domain-Specific Language)
    146. DTLS (Datagram Transport Layer Security)
    147. DTMF (Dual-Tone Multi-Frequency signaling)
    148. Dynamic typing
    149. ECMA
    150. ECMAScript
    151. Effective connection type
    152. Elemento
    153. Encapsulation
    154. Encryption
    155. Endianness
    156. Engine
      1. JavaScript engine
      2. Rendering engine
    157. Entity
    158. Cabeçalho de entidade
    159. Enumerated
    160. Escape character
    161. eTLD
    162. Event
    163. Exception
    164. EXIF
    165. Expando
    166. Fallback alignment
    167. Falsy
    168. Favicon
    169. Federated identity
    170. Fetch directive
    171. Fetch metadata request header
    172. Fingerprinting
    173. Firefox OS
    174. Firewall
    175. First Contentful Paint (FCP)
    176. First CPU idle
    177. First Input Delay (FID) Deprecated
    178. First Meaningful Paint (FMP)
    179. First Paint (FP)
    180. Função First-class
    181. Flex
    182. Flex Container
    183. Flex Item
    184. Flexbox
    185. Flow relative values
    186. Nome de cabeçalho proibido
    187. Forbidden response header name
    188. Fork
    189. Fragmentainer
    190. Frame rate (FPS)
    191. FTP
    192. FTU
    193. Função
    194. Teste de Fuzzing
    195. Gamut
    196. Garbage collection
    197. Gecko
    198. Cabeçalho Genérico
    199. GIF
    200. Git
    201. Global object
    202. Global scope
    203. Global variable
    204. Glyph
    205. Google Chrome
    206. GPL
    207. GPU
    208. Degradação graciosa
    209. Grade
    210. Grid Areas
    211. Grid Axis
    212. Grid Cell
    213. Grid Column
    214. Grid container
    215. Grid Lines
    216. Grid Row
    217. Grid Tracks
    218. Guaranteed-invalid value
    219. Gutters
    220. gzip compression
    221. Hash function
    222. Head
    223. Head-of-line blocking
    224. High-level programming language
    225. HMAC
    226. Hoisting
    227. Host
    228. Hotlink
    229. Houdini
    230. HPKP
    231. HSTS
    232. HTML
    233. HTML color codes
    234. HTML5
    235. HTTP
    236. HTTP Content
    237. Cabeçalho HTTP
    238. HTTP/2
    239. HTTP/3
    240. HTTPS
    241. HTTPS RR
    242. Hyperlink
    243. Hypertext
    244. IANA
    245. ICANN
    246. ICE
    247. IDE
    248. Idempotente
    249. Identificador (Identifier)
    250. Identity provider (IdP)
    251. IDL
    252. IETF
    253. IIFE
    254. IMAP
    255. Immutable
    256. IndexedDB
    257. Information architecture
    258. Inheritance
    259. Ink overflow
    260. Elementos inline
    261. Input method editor
    262. Inset properties
    263. Instance
    264. Interaction to Next Paint (INP)
    265. Internationalization (i18n)
    266. Internet
    267. Interpolation
    268. Intrinsic size
    269. Endereço IP
    270. IPv4
    271. IPv6
    272. IRC
    273. ISO
    274. ISP
    275. ITU
    276. Jank
    277. Java
    278. JavaScript
    279. Jitter
    280. JPEG
    281. JSON
    282. JSON type representation
    283. Just-In-Time Compilation (JIT)
    284. Kebab case
    285. Key
    286. Palavra-chave
    287. Largest Contentful Paint (LCP)
    288. Latency
    289. Modelo de layout
    290. Layout viewport
    291. Lazy load
    292. Leading
    293. LGPL
    294. Ligature
    295. Literal
    296. Local scope
    297. Local variable
    298. Locale
    299. Localização
    300. Logical properties
    301. Long task
    302. Loop
    303. Lossless compression
    304. Lossy compression
    305. LTR (Left To Right)
    306. Main Axis
    307. Main thread
    308. marcação
    309. MathML
    310. Media
      1. Media (Audio-visual presentation)
      2. Media (CSS)
    311. Media query
    312. Metadata
    313. Method
    314. Microsoft Edge
    315. Microsoft Internet Explorer
    316. Middleware
    317. MIME
    318. MIME type
    319. Minification
    320. MitM
    321. Mixin
    322. Mobile First
    323. Modem
    324. Modularity
    325. Mozilla Firefox
    326. Mutável
    327. MVC
    328. Namespace
    329. NaN
    330. NAT
    331. Native
    332. Navigation directive
    333. Netscape Navigator
    334. Network throttling
    335. NNTP
    336. Node
      1. Node (DOM)
      2. Node (networking)
    337. Node.js
    338. Non-normative
    339. Normative
    340. Nulo
    341. Nullish value
    342. Number
    343. Objeto
    344. Object reference
    345. OOP
    346. OpenGL
    347. OpenSSL
    348. Navegador Opera
    349. Operand
    350. Operador
    351. Origem
    352. OTA
    353. OWASP
    354. P2P
    355. PAC
    356. Packet
    357. Page load time
    358. Page prediction
    359. Parameter
    360. Parent object
    361. Parse
    362. Parser
    363. Payload body
    364. Payload header
    365. PDF
    366. Perceived performance
    367. Percent-encoding
    368. PHP
    369. Physical properties
    370. Pixel
    371. Placeholder names
    372. Plaintext
    373. Plugin
    374. PNG
    375. Polyfill
    376. Polymorphism
    377. POP3
    378. Port
    379. Prefetch
    380. Requisição Preflight
    381. Prerender
    382. Presto
    383. Primitivo
    384. Privileged
    385. Privileged code
    386. Progressive Enhancement
    387. Progressive web apps
    388. Promise
    389. Propriedade
      1. Propriedade (CSS)
      2. Propriedade (JavaScript)
    390. Protocolo
    391. Prototype
    392. Prototype-based programming
    393. Proxy server
    394. Pseudo-class
    395. Pseudo-element
    396. Pseudocode
    397. Public-key cryptography
    398. Python
    399. Quality values
    400. Quaternion
    401. QUIC
    402. RAIL
    403. Random Number Generator
    404. Raster image
    405. Rate limit
    406. RDF
    407. Real User Monitoring (RUM)
    408. Recursão
    409. Reflow
    410. Expressão regular
    411. Relying party
    412. Render-blocking
    413. Repaint
    414. Replaced elements
    415. Replay attack
    416. Repo
    417. Reporting directive
    418. Representation header
    419. Cabeçalho de Requisição
    420. Resource Timing
    421. Response header
    422. Web Design Responsivo
    423. REST
    424. RGB
    425. RIL
    426. Robots.txt
    427. Round Trip Time (RTT)
    428. Router
    429. RSS
    430. Rsync
    431. RTCP (RTP Control Protocol)
    432. RTF
    433. RTL (Right to Left)
    434. RTP (Real-time Transport Protocol) and SRTP (Secure RTP)
    435. RTSP: Real-time streaming protocol
    436. Ruby
    437. Seguro
      1. Safe (HTTP Methods)
    438. Salt
    439. Same-origin policy
    440. SCM
    441. Escopo
    442. Screen reader
    443. Script-supporting element
    444. Scroll boundary
    445. Scroll chaining
    446. Scroll container
    447. Scroll snap
    448. SCTP
    449. SDK (Software Development Kit)
    450. SDP
    451. Search engine
    452. Secure Context
    453. SSL
    454. Selector (CSS)
    455. Semântica
    456. SEO - Otimização dos Mecanismos de Buscas
    457. Serializable object
    458. Serialization
    459. Servidor
    460. Server Timing
    461. Server-side rendering (SSR)
    462. Session Hijacking
    463. SGML
    464. Shadow tree
    465. Shallow copy
    466. Shim
    467. Signature
      1. Signature (functions)
      2. Signature (security)
    468. SIMD
    469. SISD
    470. Site
    471. Site map
    472. SLD
    473. Sloppy mode
    474. Slug
    475. Smoke Test
    476. SMPTE (Society of Motion Picture and Television Engineers)
    477. SMTP
    478. Snake case
    479. Snap positions
    480. SOAP
    481. Source map
    482. SPA (Single-page application)
    483. Specification
    484. Speculative parsing
    485. Speed index
    486. SQL
    487. SQL Injection
    488. SRI
    489. Stacking context
    490. State machine
    491. Declaração
    492. Static method
    493. Static site generator (SSG)
    494. Static typing
    495. Sticky activation
    496. Strict mode
    497. String
    498. Stringifier
    499. STUN
    500. Style origin
    501. Stylesheet
    502. Submit button
    503. SVG
    504. SVN
    505. Symbol
    506. Symmetric-key cryptography
    507. Síncrono
    508. Syntax
    509. Syntax error
    510. Synthetic monitoring
    511. Table grid box
    512. Table Wrapper Box
    513. Tag
    514. TCP
    515. TCP handshake
    516. TCP slow start
    517. Telnet
    518. Texel
    519. The Khronos Group
    520. Thread
    521. Three js
    522. Throttle
    523. Time to first byte
    524. Time to interactive
    525. TLD
    526. TOFU
    527. Top layer
    528. Transient activation
    529. TLS
    530. Tree shaking
    531. Trident
    532. Truthy
    533. TTL
    534. TURN
    535. Type
    536. Type coercion
    537. Conversão de Tipo
    538. TypeScript
    539. UAAG
    540. UDP (User Datagram Protocol)
    541. UI
    542. undefined
    543. Unicode
    544. Unix time
    545. URI
    546. URL
    547. URN
    548. Usenet
    549. User agent
    550. UTF-8
    551. UUID
    552. UX
    553. Validator
    554. Valor
    555. Variável
    556. Prefixos vendor
    557. Viewport
    558. Visual Viewport
    559. Void element
    560. VoIP
    561. W3C
    562. WAI
    563. WCAG
    564. Web performance
    565. Web server
    566. Web standards
    567. WebAssembly
    568. WebDAV
    569. WebExtensions
    570. WebGL
    571. WebIDL
    572. WebKit
    573. WebM
    574. WebP
    575. WebRTC
    576. WebSockets
    577. WebVTT
    578. WHATWG
    579. Whitespace
    580. WindowProxy
    581. World Wide Web
    582. Wrapper
    583. XForms Deprecated
    584. XHTML
    585. XInclude
    586. XLink
    587. XML
    588. XHR (XMLHttpRequest)
    589. XPath
    590. XQuery
    591. XSLT
    592. Zstandard compression

Neste artigo

  • Aprenda mais

undefined

Um valor primitive automaticamente atribuido para variaveis que foram recentemente declaradas ou para arguments formais para qual não existem argumentos atualmente.

Aprenda mais

Conhecimentos gerais

  • Undefined value no Wikipedia

Referência Técnica

  • JavaScript data types and data structures

Help improve MDN

Learn how to contribute.

This page was last modified on 27 de abr. de 2025 by MDN contributors.

View this page on GitHub • Report a problem with this content
MDN logo

Your blueprint for a better internet.

  • MDN on Bluesky
  • MDN on Mastodon
  • MDN on X (formerly Twitter)
  • MDN on GitHub
  • MDN Blog RSS Feed

MDN

  • About
  • Blog
  • Careers
  • Advertise with us

Support

  • Product help
  • Report an issue

Our communities

  • MDN Community
  • MDN Forum
  • MDN Chat

Developers

  • Web Technologies
  • Learn Web Development
  • MDN Plus
  • Hacks Blog
  • Website Privacy Notice
  • Cookies
  • Legal
  • Community Participation Guidelines

Visit Mozilla Corporation’s not-for-profit parent, the Mozilla Foundation.
Portions of this content are ©1998–2025 by individual mozilla.org contributors. Content available under a Creative Commons license.