n. What is seen when a topless woman (or very fat man) turn far enough to the side to see the breast, but not the nipple. Many movies, in order to keep a PG-13 rating, show only side boob. Braless women who wear sleeveless t-shirts are notorious for side boob.
"My roommate's girlfriend was wearing his muscle shirt without a bra. It was side boob city."
The side view of a female breast that is usually unintentionally exposed by a female wearing a loose shirt or revealing bathing suit. Arguably almost better than actually seeing a fully exposed breast, the sideboob is the "profile" of a breast without exposure of the nipple. The side boob gives you a great sense of what you are working with while also keeping it PG-13.