As relates to texture atlases, what is a “quad”?

Question

It is my understanding that a texture atlas is basically a single texture that contains many smaller textures and that they are useful for making games or animations faster because they allow you to access many animation frames by loading a single file rather than files for each and every frame.

So, in discussions of texture atlases, I see the term "quad" mentioned everywhere - Is a quad simply the x, y, width and height of an individual texture from a texture atlas or am I missing something?

Answer 1

Quadrilateral - not necessarily a rectangle.