Sub Textures

You already know how to texture atlas. When you use an atlas you have a large image that's packed with smaller images. You access those images by modifying the uv coordinate that you draw.

Sub-Textures is almost the same thing. With sub-textures you can load sections of a texture as their own texture handles, essentially making them new textures.

This feature is mainly deamed to be useless, not many people use it. Especially for games.