First popularized by the "Professor Brothers" cartoons.
Ian: "Bro Grab, man."
Mike (suddenly comfortable and unmolestedly): "Ah. Cool."
"I pulled up to the curb with manly, Kate Moss confidence. And there's the dean and his wife, bulging with impatient fluids. I moved in for a bro grab and got totally whiffed" - Professor (ep. 'Late Date')
In this context it is describing two actual brothers hugging, but can be used for african americans or just if you hug one of your bros.
Far more manly than a hug but less manly than breaking bits of wood with your head.