What does OB mean in golf?

Answer 1

This stands for out of bounds. It is an area of the Golf course or off the golf course which is not in play. If you hit your ball out of bounds, you cannot play your next shot from there, you must re-hit your shot from the place you originally played from. There is a one shot penalty for hitting out of bounds.

Answer 2

It is the shortened term for out of bounds.