A common term used most recently around South Florida but has spread to many other influential areas of the world. It refers to a person who, by law, is considered to be a step-brother; however often times thought of by one (or both parties) to be more of a true brother and almost related by blood.
Girl 1: "Ooh, look at that hot guy. Maybe I should go buy him a drink"
Girl 2: "Back up hoe. That's my stebro. One drink ain't gonna change your dog face either!"