The surfboard maneuver that turns sharply at the bottom of a wave is called a bottom turn.
A bottom turn is usually the first major turn after a surfer drops down the wave face. The surfer compresses, applies pressure to the rail, and redirects the board upward toward the open face or the breaking section. The maneuver converts the speed gained during the drop into a controlled line across the wave.
Bottom turns vary according to the wave and the maneuver that follows. A surfer may use a longer, drawn-out bottom turn for a powerful top turn or a tighter turn in a small pocket. Rail control, body position, and timing all influence the result.
A bottom turn is different from a cutback, which redirects a surfer back toward the breaking part of the wave after traveling away from it. Both are turns, but they occur in different parts of the ride.