It means the KKK (Ku Klux Klan) which was an American white supremacist hate group. The reason 3 11 stands for 3, 11s with 11 being a K, the eleventh letter of the alphabet.
Guy 1: Yoo how do we talk about the KKK without sounding sus?
Guy 2: How about we come up with some secret code with letters from the alphabet and numbers?
Guy 1: I guess we could do 3 11.
Guy 2: How does that mean KKK?
Guy 1: 3, 11s with 11 being the eleventh letter of the alphabet.
Guy 2: Oh that makes sense. Speaking of which should we join the 3 11.
Guy 2: How about we come up with some secret code with letters from the alphabet and numbers?
Guy 1: I guess we could do 3 11.
Guy 2: How does that mean KKK?
Guy 1: 3, 11s with 11 being the eleventh letter of the alphabet.
Guy 2: Oh that makes sense. Speaking of which should we join the 3 11.
by Pork on a Stick December 8, 2019
Get the 3 11mug. that was the day when the Discord Staff messed with teenserv and locked the RAM allocation for teenserv. Messages that were sent in chat were dead slow and shit wasn't fixed until it was 6/12.
man, all these days ending with 11s, 4/11, 5/11, 6/11, they do be crazy as hell, especially the 6/11 one, that one was from the discord staff themselves.
by johntobasco June 11, 2020
Get the 6/11mug. 
by Mate4 November 10, 2019
Get the November 11mug. by Qwrety3 December 6, 2020
Get the December 11mug. by Retorted guy October 24, 2019
Get the 9/11mug. by JD ORKA May 10, 2020
Get the October 11mug.