The phrase "player coop" usually refers to a multiplayer video game mode where two or more players work together or cooperate to achieve a common goal in the game. Full definition
More Titanfall 2 DLC is incoming in the form of a 4 player coop mode called Frontier Defence as well as 2 new maps and more customisations! (gameondaily.com)
The problem with moving three characters around in a game that was designed for 3 - player coop play makes the game quite tedious in some parts. (nintendoenthusiast.com)
The game is described as a single player coop game. (xbox-360.co.za)