It's slang used in Atlanta, standing for Out The Perimeter. Out the perimeter is outside of I-285, which surrounds DeKalb County, hosting the city of Atlanta.
ATL Nigga 1: Aye ain't Johnny from Covington?
ATL Nigga 2: Yea, that bum nigga OTP, fronting like he from Decatur
ATL Nigga 2: Yea, that bum nigga OTP, fronting like he from Decatur
by Bummies November 22, 2018