Overview
In professional wrestling, a pin is a move where a wrestler holds an opponent's shoulders to the mat. A pinfall is a common victory condition, where the attacker pins an opponent and the referee makes a three count before the opponent gets released from the pin.
Background
The origin of the pinfall is the pin from amateur wrestling, whereby pinning an opponent to the mat will result in an automatic victory despite any points scored. However, while an amateur wrestling pin need be only one or two seconds, the count in professional wrestling is based on the referee's arm gestures, regardless of how much actual time elapses, and is to three slaps of the mat.
The count is broken (a near-fall) if the opponent manages to raise one or both of their shoulders off the mat, commonly by kicking out (throwing their legs up to cause their shoulders to rise from the mat). In some positions, a wrestler may bridge (arching their back so that only their feet and the top of their head are touching the ground) to put more of their weight on the pinned opponent or to prop themselves up from being pinned.
From Wikipedia (CC BY-SA 4.0).