To let the person you're talking to know that you are being serious. To keep it real. No fakeness. No lying. Be truthful.
One hun'ed is the correct spelling BC no one says one hundred. Hun'ed sounds more like hunted without the "t" so these should be an apostrophe in its place.
DJ: Yo. One female, she looks familiar, dude. She real looking familiar, man. You know you my boy. We keep it one hun'ed. We savages. We grimy. You already know what it is my dude.
Ray-J: Which one!????
Ray-J: Ahhh. She smashed the homie! ....... Thanks for keeping it one hun'ed with me my dude.
DJ: I got you.