This refers to substantial loss of hair on one side of man's head.
In the earlier stages of male pattern baldness,
men can lose a lot of hair on the peaks of their heads. When this receding occurs at an alarming
rate on one side of the head, it is known as a
Harrison's Peak.
The effect is to leave the man with a gaping chasm on the peak of the head, which they often attempt to disguise with inventive new haircuts.