Co-op is short for cooperative play. It means two or more players work together toward a shared goal, such as finishing a mission, surviving a wave, solving a puzzle, or defeating a boss.
Local and online co-op
Co-op can happen on the same screen, through split-screen, over a local network, or online. Some games are built entirely around cooperation, while others offer co-op as an optional mode.
Why co-op changes a game
Co-op adds communication, teamwork, role sharing, and rescue moments. A difficult challenge can feel more manageable when players divide responsibilities.
Co-op is often used in PvE games, but some games mix cooperation and competition in the same session.