Or, Butch-Bitch relationship, is a relationship where one partner is domineering and the other just submits to whatever they say or do. Much like the caricature of a caveman dragging a woman by her hair to his cave, it's usually characterized by a macho guy who finds an intelligent, attractive woman, and by brute force takes over her life.
It's more commonly used to describe lesbian relationships, where the couple feels the need to mimic this typical heterosexual dynamic.
Harry Potter's aunt and her husband are a familiar butch-bitch relationship. The husband flares up anytime anything threatens the sanctity of his life, and the wife just looks withdrawn and frightened.
Also there's the stereotypical lesbian relationship where a petite, attractive "femme" will date a woman in flannel and a mullet.