A constant velocity (CV) joint is a type of mechanical joint used to connect the drive shaft of a vehicle to its wheels. The purpose of the CV joint is to transmit torque from the engine to the wheels while allowing the wheels to move up and down and steer from side to side.

The CV joint is designed to provide a constant velocity of rotation, regardless of the angle at which the drive shaft is operating. This is important because the angle of the drive shaft changes as the suspension of the vehicle moves up and down, and as the wheels turn left and right during steering.

There are two main types of CV joints used in vehicles: ball-type and tripod-type. The ball-type CV joint consists of a spherical housing with a set of bearings inside that allow the joint to move in multiple directions. The tripod-type CV joint has three prongs that fit into slots on the joint housing, allowing the joint to move up and down and side to side.

CV joints are subjected to a lot of stress and wear over time and may need to be replaced if they become damaged or worn out. Symptoms of a damaged or worn CV joint can include clicking or popping sounds when turning, vibration during acceleration, and grease leaking from the joint. Regular maintenance of the CV joint, such as checking and replacing the grease, can help prolong its life.