It's the male counterpoint to MILF, like Brad Pitt to Angelina Jolie. People who've retained their hotness in spite of being a parent, or even +200 hotness points on somehow successfully juggling their individuality (pod parents people are scary) without pretending they never had kids and being completely irresponsible and neglecting to parent (Britney Spears, probably her mom, in addition to Paris Hilton's mom).