Mods (short for modifications) are changes made to a game by its community or developers to alter or enhance gameplay, add new features, or modify existing ones. In the context of WWE 2K17, a mod inspired by or incorporating elements of Wrestling Revolution 3D would theoretically aim to bring aspects of the latter game's gameplay or features into the former.
If you have played a console WWE game, WR3D plays very differently. It does not use the thumbstick "grapple" system of 2K games. It uses MDickie’s unique control scheme: wrestling revolution 3d wwe 2k17 mod download