A fully shaved pubescent region, such as a vagina, or penis/scrotum. The term can also describe the head. The term is used in a derogatory fashion, or amidst hyperactive behaviour.
"Did you see Peter's head??"
"Yes! he's gone for the shaven-haven!"
A hairy mary refers to the growth of a women's pubic hair surrounding the vagina whereas a shaven haven is when there is no hair at all due to shaving, waxing or laser therapy. 'Hairy Mary' tens to be made fun of as the name connotes virginity and lack of beauty when in actual fact either amount of hair can be favoured.
Sam: I can't choose between a shaven haven or hairy mary.
Michael: Well you can have them bare like the magazines or natural like the rest of us, but I don't think you can choose those things about a girl mate.