A sexual position similar to 69. In 63, the girl is on top, and instead of giving the guy head while he eats her out, she lets him titty fuck her. The outline of her boobs is like the number 3.
Girl #1: wow did you 69 him last night?
Girl #2: nah i was feeling a little lazy so we did some 63.
A slang way of saying down syndrome, usually used to insult someone. Derived from the fact that down syndrome is caused by 3, 21 chromosomes.
(3*21=63).
Wow, just look at connor, that kid fails so much he gotta be a 63
by katana90 March 30, 2011
Refers to a tricked out (luxury) 63 chevy impala from the west coast with nice hydraulics.
My Man be rolling down the avenue in his 63 every night.
by Amy9999 July 10, 2006
When you get a little bit of this, with a little bit of that.
Dude1: "hey dude, i got 63 coming my way."
Dude2: "let me in on that."
by Lumbuxia October 21, 2009
A tricker position than 69.

The guy is standing up while he’s inserted into the girl who is reverse cowgirling and bends her body forward to eat out his ass.
Damn you need a lot of stamina to 63, I bout dropped my bitch on her head”
by Hoe White October 16, 2017
(Internet slang, fandom slang, informal) The proposition that it is possible to find genderswapped versions of every fictional character, especially as fan arts on the internet.
This kid likes Rule 63
by Oofbaby June 2, 2018