From Quake Wiki
cvar is a developer command that shows the outlines of world and object polygons as triangles. It is helpful for optimizing geometry and vis-blocking.
It has three posible states 0 to 2
- 0: Disable this feature.
- 1: Enables it like in the picture.
- 2: Also enables it, but it won't show what's rended behind a wall like 1.