Hot mom means sexy mom; deduce that to mean mom I'd like to have sex with; regard that statement as
Mother I'd Like to Fuck, hence the terminology:
MILF.
Joey: Wow, Ross, your ex-wife Carol is one hot mom.
Ross: You're talking about my son's
mother.
Joey: Hey, I call 'em as a I see 'em. I'm sure Susan
will agree that she's a
MILF.
Ross: Shut up!