Navigation mesh used by games developed with the id Tech 3 game engine or a derivative of the id Tech 3 engine such as Valve's Source Engine; saves a mesh of walkable areas within a .BSP map file; allows artificial intelligence (AI) bots to know how to move around the map.

NAV files are automatically generated by the game engine when a user first plays a map with bots. The loading process may take several minutes for large maps. You can manually start the NAV generation process by typing nav_generate in the game console. You can also edit navigation meshes manually by typing nav_generate 1 in the game console while "sv_cheats" is enabled. NAV files are similar to .AIN files, but AIN files are more commonly used for non-player characters (NPCs) instead of bots. NOTE: Example games that use NAV files include Quake 3 (id Tech 3 engine), Counter-Strike: Source (Source Engine), and Team Fortress 2 (Source Engine).