In 3D graphics, a texel is a single pixel within a texture. Textures are images presented on a polygon's surface within a 3D rendered image. A texture is characterized by a collection of texels, similar to how an image is characterized by a collection of pixels.
A pixel in a raster image file is a series of bits containing color data, and sometimes opacity data, which maps to display pixels on an output device such as a computer monitor. When a pixel belongs to an image used as a texture resource, it is called a 'texture pixel' or shortened to 'texel'. Instead of mapping directly to screen pixels, a texel's data is mapped to a location in the coordinate space of the 3D object being modeled. Textures can be used to convey color and other surface qualities such as depth and reflectivity. Multiple textures may be layered to create complex surface overlays.
The process of mapping the appropriate texels to their corresponding points on a polygon is called texture mapping. Texture mapping is a stage of the process of rendering a 3D image for display. When the source texel grid and destination pixel grid do not align, further texture filtering is applied to smooth the resultant texture-mapped pixels (texture magnification or minification). The final output of the rendering process is a flattened 2D projection of the 3D model, where the texture has been 'wrapped' around the model.
During the render pipeline, texture mapping is typically done prior to lighting the scene; however, in WebGL, lighting is performed as part of the texture mapping process.