A bacteriophage, also called a phage, is a virus that infects bacteria. The term “bacteriophage” means “bacteria eater” (from the Greek word phagein, which means “to devour”). Phages consist of a long nucleic acid molecule (usually DNA) coiled within a polyhedral-shaped protein head. Many phages have a tail attached to the head. Fibers extending from the tail may be used to attach the virus to the bacterium.