Literally, "Your" (n.) - 'an English word that is used when one person is talking to another and they want to refer to the person they are talking to in a 1st person point of view' + "Mother" (n.) - 'an English word that describes a female of a certain species that is or was capable of sexual reproduction at some point in their lives and exercised that aspect of their lives, and caused the creation and growth of a fetal offspring in their womb, egg, or pouch'; therefore, "Your" + "Mother" = the mother of a creature that a person who speaks English is referring to in a 1st person point of view. Don't you just love these literal definitions to just irritate the hell out of people?

A silly phrase which is often followed by a completely unfunny jibe. Often used by idiots online who can't think of these things spontaneously.

Joke Time: If I had half-a-penny for every brain cell that yo mama didn't have, I'd be richer than Bill Gates!

Something that provokes jokes. YO MAMA!
Something you say if someone asks you what you wanna do. YO MAMA!

That fat smelly bitch who cooks me dinner and licks my ass...

Not my mama.

Your mother;Defense against insult, as in