Term that originated in California used in predominantly Black or Latino hoods/gang culture. Derived from the Spanish word loco. "Loc" referring to a person or "loc up" is a variation of the Spanish word loco.
Short for loco, which in Spanish means crazy (loca is female; loco is male). Loca could have literal meaning (someone who actually lost his/her mind), or metaphorical meaning referring to someone who is wild and does unexpected things.
Cali has a strong Mexican/Hispanic culture, we all get down with aspects of the same terminology.
What up Loc!?
To my niggas in the penitentiary, Loc up, like a mothafucka, when they mention me, ' Cause you fuckin' with the realest mothafucka ever - Tupac, Straight Ballin