Walkmesh

The term walkmesh refers to the surface of an area which a character can actually walk over. Obsticles, trees, buildings, rocks, and placeables all create "holes" in this walkmesh where you cannot travel.

Static placeables create holes in this walkmesh when the area is being compiled, whereas non-static placeables dynamically effect the walkmesh during the game when a character is attempting to walk near it (Being non-static means you cannot guarantee it will be there all the time).