A special texture that when applied to a brush makes an invisible line to cut a VIS leaf into 2 or more parts, to control line-of-sight and reduce wpoly counts. HINT is usually used on only one face of a brush, the rest of the brush is textured
SKIP.
For best effect, a HINT/SKIP brush should be placed so that it cuts across a corner between two hallways.
Have a look at
Andy's tutorial for more information.