short for "nippleslip". When a female nipple or at least the areola is showing, its called a nipslip.
Paris Hiltons nipple showed again, she had a nipslip.
when you're wearing a shirt with out a bra and your nip slips out and you can see it and the public is like "WTF, YOUR NIP IS OUT!"
dude your nip is out, wtf its a nipslip.