A "Texture Hack" is a Mario Kart Wii track in which the Textures have been changed, but the model and layout of the track remain the same. People who are learning how to make Custom Tracks sometimes make texture hacks first, since they're much simpler to create.
Some tracks have changes made to both the textures and objects, changing gameplay, but the model still remains the same. Those are known as custom tracks without model edits. Template:Texture Hacked Track List