A standard competitive Counter-Strike team has five players.
The classic competitive format is five versus five, usually written as 5v5. One side plays terrorists and the other plays counter-terrorists, with the teams switching sides during a match. The format gives each player enough responsibility for individual skill while preserving coordinated team tactics.
Teams commonly divide responsibilities informally among roles such as entry fragger, support, lurker, in-game leader, and AWPer. These are strategic descriptions rather than fixed character classes. Players can buy different weapons and equipment each round, so roles may change according to the economy and map situation.
The answer is sometimes confused with the total number of players. A full standard match contains ten active players, but each team contains five. Other modes, including casual, deathmatch, wingman, and custom servers, can use different player counts.