Composed of two words, jack and off. See those for the individual meanings.
I helped my uncle Jack off his horse.
by N. 1. August 26, 2006
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Male masturbation; a man rapidly and repeatedly rubs his hand up and down his dick until he hits orgasm.

Done when horny, when porn is plentiful, or to get rid of a boner in class.
Jason had a huge boner in science class, so he ran to the bathroom. But there were a whole bunch of other kids with their pants and boxers around their ankles and their dicks in their hands, masturbating furiously.

There were three guys at each of the urinals, one on each toilet and two more standing in front of each. There was another pair at each of the two sinks, and at least fifteen spread out across the floor. They all groaned as they shot their loads across the room.

"It's a jack off epidemic!" Jason stood wide-eyed as his dick stretched hard against the fabric. He quickly dropped his jeans and plaid boxers and began to jack himself off in the doorway.

More guys pushed against him, trying to get some privacy to jack off in. He felt three dicks strain against his back.

He felt his dick grow larger and larger as more guys pressed against his ass.

Then he woke up. He looked down at the puddle of sperm in his hand, then quickly pulled his boxers back up and laid down to sleep.
by HornyGuy2 March 03, 2009
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To grab the hard, erect penis and rub it in a firm motion up and down until it turns red and is towards the point of ejaculation.
I haven't jacked-off in a while. So I'm gonna make up for loss time and jack-off for 18 minutes straight.
by Bentropelex November 23, 2003
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Causes Pleasure and Anger. The pleasurable part is pre-ejaculation. The Anger part is post-ejaculation. This is the part where the man becomes mad at himself for wasting 30 minutes of his time. The world suddenly becomes clear and the chemical imbalance is one again balanced. Too bad no man learns this lesson and history repeats itself.
I had a great time jacking off, up until the end.
by Patrick April 23, 2008
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rubbing the penis so he spits up his cum
what I'm doing as I'm writing this, oh man just ejaculated everywhere
by I'm jacking off September 07, 2003
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when a guy rubs his big throbbing cock cuz he can't put it in my pussy cuz i am too busy rubbing it to notice him
by sexybabe August 21, 2003
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To masturbate until the point of ejaculation is reached.
Oh, oh, ho, oh my god, wait.. wait a..., oh OH SHAZAAAM!
by gabe April 21, 2005
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