A group of musicians specializing in rock music is called a rock band or rock group. Many rock groups consist of an electric guitarist, lead singer, bass guitarist, and a drummer, forming a quartet. Some groups omit one or more of these roles or utilize a lead singer who plays an instrument while singing, sometimes forming a trio or duo; others include additional musicians such as one or two rhythm guitarists or a keyboardist. Rock bands from some genres, particularly those related to rock's foundations in rock and roll, include a saxophone. More rarely, groups also utilize bowed stringed instruments such as violins or cellos, and brass instruments such as trumpets or trombones.