The base leg is that portion of the airport traffic pattern along which the airplane proceeds from the downwind leg to the final approach leg and begins the descent to a landing. While on the base leg the pilot must accurately judge the distance in which the airplane must descend to the landing point and correct for wind drift so the ground track remains perpendicular to the extension of the centerline of the landing runway.
The final approach is the last part of the traffic pattern during which the airplane is aligned with the landing runway or area, and a straight line descent is made to the point of touchdown. The descent rate (descent angle) is governed by the airplane's height and distance from the intended touchdown point, and the airplane's speed over the ground.
The roundout, or flare as it is sometimes called, is that part of the final approach where the airplane makes a transition from the approach attitude to the touchdown or landing attitude.
The touchdown is the actual contact or touching of the main wheels of the airplane on the landing surface, as the full weight of the airplane is being transferred from the wings to the wheels.
The after landing roll, or rollout, is the forward roll of the airplane on the landing surface after touchdown while the airplane's momentum decelerates to a normal taxi speed or a stop.