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3.
To commence to do something. Usually in an excited manner.
" i jam out then commence to bust the skeet-wave."

guy 1: hey man, what you bout to do?
guy 2: Man!, i'm bout to jam out on this new game I got.
guy 1: word?! I'll come too!
by Sir Nise May 03, 2006
 
1.
jam out: verb; means to relax, unwind, rest, chill out, etc, etc.
Pimp: Ey man, whats good? Where all da hunnies at?

Playa: Aint nothin poppin forreal, its cold so Imma stay my ass at home and jam out.

Pimp: hahaa yea its cold as a muthafuc*a aint it? Imma make da hunnies come to me, ya feel me? aight, man 1.

Playa: Aight B, 1.
by thisonechick February 16, 2006
 
2.
to suddenly stop, to fail at the last minute, to cancel plans for other reasons.
I thought we had plans Thursday, why did you jam out on me? I was following to closly to the car infront of me when her breaks jammed out; I couldn't stop in time. The drill press at the factory has jammed out again; coffee break time.
by Grjohnstone October 09, 2006