Also called a Serial or Harvard Comma, it is a punctuation used immediately before a grammatical conjunction. Ezra Koenig, Rostam Batmanglij, Chris Tomson, and Chris Baio (Oxford Commas are used between the names.)

But the preppy indie band Vampire Weekend also uses the term to refer to a white, preppy guy from Oxford, as "comma" has also been used as slang for an obnoxious white person.
by Kylieeeeeee. April 26, 2008
A sexual position in which both parties are laying on their sides, bodies in the shape of commas. In order to be classified as an "oxford comma", this must be performed with someone who is attending or has attended an Ivy League institution.
HARVARD MAN 1: Hey man, how was that party last night?
HARVARD MAN 2: Dude, I oxford comma'd the shit outta that girl.
by Tylaire June 19, 2020
an oxford comma is a small curly-que of a turd squeezed out onto your dick when you are fucking a girl doggy-style.
so i was fucking your sister last night and when she came she gave me an oxford comma.
by magnitogorsk May 3, 2010