A class based shooter is a game that gives players a variety of different character class-builds to fit each situation. They were added into shooters such as Call of Duty, Borderlands, and Mass Effect in order to add more strategy and depth to the gameplay.
These classes are normally reserved for attacking enemy objectives, whether it's capturing a flag or control-point, or carrying the bomb to an enemy bomb-site.
The basic assault unit, whose weapon of choice is normally an assault-rifle. Possesses high mobility.
This unit is designed to reach objectives undetected by enemies, and are usually accompanied by perks that keeps them hidden from radar. Also, usually a close-quarters combatant like the Light Infantry unit.
Normally reserved for games that emphasize vehicles, these people are resourceful at piloting land or aerial vehicles to attack enemy objectives.
These classes are reserved for defending objectives, whether it's the team's own flag or flag-carrier, a control point already being held, or a bomb-site or bomb-carrier.
Focuses on heavy weapons such as the light-machine gun to defend objectives from a distance. Slower than the light infantry class, but compensates for higher range and firepower.
Emphasizes attacking enemies at a great distance with a sniper-rifle. Like the CQB class, usually emphasizes stealth.
This class is about destroying land vehicles or aircraft, in order to ensure that they do not reach their objectives. Again, normally reserved for games that emphasize vehicles, like the Battlefield series.
Compared to the usually offensive or defensive classes, these classes emphasize supporting the team, rather than either attacking or defending enemy objectives.
Resourceful for repairing vehicles or defensive structures. Like the driver/pilot and anti-vehicle/anti-air units, usually reserved for games featuring vehicles. And if any time there aren't any vehicles, it's just building and repairing fortifications.
Designed to restore lost health of allied units, as well as revive them upon falling.