ur mom

1. Ur mom, also your mom or your mum, is commonly used as a random phrase.

2. Ur mom, also yo momma or yo mama, is a joke made often. Usually, the person telling the joke is not trying to insult the receiver's mother.

3. Ur mom is the dead woman whom you're insulting. Even though you didn't mean to, you still insulted her.

1. literally any teacher: "Please read the next paragraph."
nervous me: "Uh.. uh.. UR MOM!" *runs out of class in fear*

2. joke teller: "Ur mom's so fat she couldn't even enter Walmart!"
receiver: *laughs nervously*

3. joke teller: "Ur mom's so stinky even the garbage couldn't handle her!"
receiver: *tearing up* "Dude, my mom's dead.."