There is only one file type that uses the .WEAP extension:
Quake 3 Engine Weapon File
Weapon description file used by id Tech 3 (Quake III engine) games; contains plain-text definition for game weapons, including 3D models, animations, sounds, and the weapon icon; often used by game modification packages to store custom weapons.
WEAP files can often be found within .PK3 game archives.
Updated: March 31, 2010