GKD is a slang term for a
general population prisoner. It stands for “Gangstas, killas, and dope dealers”, which is what usually makes up
general population, whereas
Protective custody and maximum security tends to be made up of more sex offenders, rapists, and mentally ill prisoners, etc.
The term comes from the song “The Gangsta, The Killa and the Dope Dealer” by Westside Connection.