This phrase is used (mostly in England) as one of the best way to end a conversation. The reason for this is because there is no way to reply to it.
Example 1:
Joe: What do you want for dinner tonight?

Jeff: Ur mum

Example 2:
Bob: Harry you’re so ugly

Harry: Ur mum

Example 3:
Teacher: Harvey, did you do your homework?

Harvey: No

Teacher: Why not?

Harvey: Ur mum
by Ur mum definition February 18, 2022
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the words 'ur mum' are the greatest words mankind has ever invented. There is so much emotion in these beautiful words I cannot even describe how it makes me feel when someone whispers these words Into my ears it makes me feel all buzzy and tingly it is a sensational feel coursing through your body. the maker of these words a quandarius figgle bottom the 3rd now he is the most gorgeous person to ever set foot on this earth gosh I wish he would marry me.
jack: Hey christian ur mum is a fucking ugly whore.
Christian: shut up cuz guess what I had intercourse with ur dad last night
jack: wha-
by Yo_mamaOffical June 3, 2022
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Someone British trying to roast you, but it doesn't sound good because they can't say ur mom.
British person: Ur mum is weird.
Me: Stop trying to roast my "mum".
by oh um okkk April 9, 2021
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The way to answer anything or start an insult, it's even better if who you're talking to doesn't have a mom or their mom is dead.
mainstream kid: Hey what's your favorite fortnite skin?
me irl: ur mum xdddd

kid: M-my mom is dead.... *breaks into tears*
me irl: tHaTs HiLaRiOuS *does fortnite default dance*
by Walaba September 29, 2018
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The most kiddish yet widely used insult ever.
"lmao i fukd ur mum"
by TheRothead December 24, 2016
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