Green’s Dictionary of Slang

new jack adj.

[new jack n.]
[1980s+] (US black)

1. superficial, flashy, meretricious.

2. in tune with the contemporary young black culture.

3. naive, unaccomplished.

In compounds

New Jack City (n.)

[1990s+] (US black) Detroit, New York City or any other city with a thriving ghetto lifestyle.