Cooperative is a game type in Guitar Hero, Guitar Hero II, Guitar Hero III: Legends of Rock, Guitar Hero Encore: Rocks the 80s, and Guitar Hero: Aerosmith. As the name suggests the game type is played by two people as opposed to one. In later games cooperative is replaced by full band play.
Cooperative can be played in Quickplay, or Career. In Cooperative gameplay the two players are working together so the Star Power Meter, Rock Meter, Note Streak, and Points Meter are shared. For Star Power to be activated both players have to activate withing the same time period. While playing a song the two guitarists are either lead and bass or lead and rhythm.