in The second nine holes as opposed to out - the first nine holes
inland - in play Within the course (not out of bounds).
inside Being nearer the hole than the ball of your opponent.
interlocking grip A type of grip where the little finger of the left hand is intertwined with the index finger of the right hand for a right handed player. The converse applies to a left hander.
intended line The line you expect the ball to travel after hit.
iron Any one of a number of clubs with a head made of iron or steel. See definitions for individual clubs "two iron" etc.