The best asset of a female. Other related words would be: Boobs, breasts, titties, knockers, fun bags. A cooler word for tits which the female species does not detect, thus allowing men to say tatums in public w/o being slapped.
A Tatum is a girl who is really easy to talk to. The best use for a Tatum is to bring her along on a "date" to prevent awkward silences if you're still uncomfortable with your the girl you like. She takes all the tension or awkwardness out of the "date".
"I was super nervous about my date with Jessica, but then i brought this Tatum i met at swim class along and it went really well"