Release
The natural unhinging of the wrists through impact that squares the clubface and delivers speed to the ball.
A natural release is different from actively "releasing" the club with the hands, forcing extra rotation through impact usually shows up as a flip or an early cast instead of added speed.
More swing mechanics terms
Address
The setup position a golfer takes before starting the swing.
Takeaway
The first foot or two of the backswing, as the club first moves away from the ball.
Backswing
The motion from address to the top, where the club is loaded before the downswing.
Top of the Backswing
The highest, furthest point of the backswing, right before the downswing begins.
Transition
The change of direction from backswing to downswing.
Downswing
The motion from the top of the backswing down through impact.