Nothing. Used to describe what a person is incapable of doing or what a person has no clue about either by learning or experience.

Broadly equivalent to Jack Shit, Diddly Squat, etc.
Guy1: I know that Obama is a communist and a muslim. He is also not a citizen.
Guy2: Yeah, what's your name?
Guy1: Jack
Guy2: Yea, Jack. Don't know Jack.
by blueliner49 February 8, 2010
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The mist ignorant dushy guy on the planet. He is super annoying and won't leave you alone ever. He can't stop talking and will always stalk you. If you ever meet a guy like jack don't like him. (HIGHLY ATRACTIVE)
Damn that jack is sexy

Ya but he is a total dush.
by californiagirl11 February 5, 2010
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A very common Australian nickname for police men.
Oh no, Jack! A jack just jacked my jacket. What a jackass.
by schase10353 December 31, 2010
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Guy One: "Man did you see that Jack earlier?"
Guy Two: "Oh yeah, he's a POWERtool."
by anon23987456310 December 14, 2013
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A jack-ass
Hey Jack is a jack-ass!
by Crazy lamp July 28, 2017
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Jack is a disrespectful person, who you can't trust. He will turn on you. He is gay as anything. He gets jealous easily and he is a pure cunt. He doesn't deserve to live. He cannot be a friend without him teasing, bullying you.
by The_True_Man__ August 28, 2017
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