The word "newjack" is another term for "newbie" or "noob". It means one who is new to something and lacks experiance and style in it.

A word adopted by rappers, however this originally is derived from prison slang and refers to a person who is new in prison.

Short for the word New Jack Swing, used för the music genre that had its biggest years in the late 80's until the mid 90's. It is a hybrid of R&B and sounds like hip hop with a more "swinging" sound on the beats, with the r&b style of singing.

Teddy Riley is said to be the father of New Jack Swing, also Tony Toni Toné, Johnny Gill, Gerald Levert, Bobby Brown, Blackstreet, New Edition and Guy were big names in the New Jack era.
The movie New Jack City (1991) also contains a lot of New Jack Swing music.

Hip-hop slang for an overly energetic, almost buffoonish rapper. Originated in the early 1990's with such mainstream hip-pop acts as Kid 'N Play, Salt N Pepa, and Bill Bev Devoe. This "New Jack Era" lasted for a few years, but was quickly supplanted by the rise of West Coast-styled "gangsta" rap, as exemplified by NWA (and, more recently, Westside Connection). In an earlier era, "new jack" also referred to any novice on the microphone, usu. with a distinct lack of lyrical talent.

an individual whos new to a scene who may or may not really be into it, as in they may or may not be a poseur but are still ridiculed for being a late comer.
a new jack can also be some one who all of a sudden became "interested" in a scene and the next day dress as best they can to fit into the scene.

former ecw wrestler

person who tries to fit in the scene
when the scene doesnt want him; when a person puts bands on myspace that hes never heard of but claims to listen to; when he swapped an iron cross for a paul frank shirt.