Release
The point in the downswing at which the wrists uncock. A late release (creating "lag") is one of the keys to a powerful swing.

Rough
The grass that borders the fairway, usually taller and coarser than the fairway.

Rub of the Green
Occurs when the ball is deflected or stopped by a third party/object, e.g. if a ball is going out of bounds and is deflected in bounds by hitting a spectator or a tree.

Rutter
A small headed niblick for hitting the ball from a cart track.