TLD (トップレベルドメイン)

TLD (トップレベルドメイン)は、インターネットの階層的な DNS (ドメインネームシステム) で最も一般的な domain です。TLD は domain name の最後の要素です。例えば、developer.mozilla.org の "org" です。

ICANN (Internet Corporation for Assigned Names and Numbers) designates organizations to manage each TLD. Depending on how strict an administrating organization might be, TLD often serves as a clue to the purpose, ownership, or nationality of a website.

Consider an example Internet address: https://developer.mozilla.org Here org is the TLD; mozilla.org is the second-level domain name; and developer is a subdomain name. All together, these constitute a fully-qualified domain name; the addition of https:// makes this a complete URL.

IANA today distinguishes the following groups of top-level domains:

country-code top-level domains (ccTLD)

Two-character domains established for countries or territories. Example: .us for United States.

internationalized country code top-level domains (IDN ccTLD)

ccTLDs in non-Latin character sets (e.g., Arabic or Chinese).

generic top-level domains (gTLD)

Top-level domains with three or more characters.

unsponsored top-level domains

Domains that operate directly under policies established by ICANN processes for the global Internet community, for example "com" and "edu".

sponsored top-level domains (sTLD)

These domains are proposed and sponsored by private organizations that decide whether an applicant is eligible to use the TLD, based on community theme concepts.

infrastructure top-level domain

This group consists of one domain, the Address and Routing Parameter Area (ARPA).