Lag
Retaining the wrist hinge deep into the downswing instead of releasing it early, storing up clubhead speed for impact.
More lag generally means more effortless power. The opposite of lag is casting.
See the full breakdown: Thin / Skulled Shot
Every common cause and fix for this exact issue.
See the full breakdown: Weak / Short Shots
Every common cause and fix for this exact issue.
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.