First person shooter games (or fps games as everybody calls them) are a popular "genre" of game, but not every fps is some variation of "Battlefield" or "Call of Duty". There are some outliers.
The basic requirements for being a first person shooter, is that the game is played in the first person, and that you shoot something. Most if not all of these games are played online with other people, but there are the occasional single player first person shooters. The first non "shooter" fps I played was probably Portal.
In Portal the only gun you have is the Aperture Science Handheld Portal Device (or just "portal gun" if you're so inclined). The only thing this gun shoots is portals, not bullets.
The gameplay built around this mechanic is unique and mind-bending. Portal is a must-play for anybody interested in video games, especially first person shooters.