A musical genre which originated as rock and roll in the United States in the middle of twentieth century, developing from blues music. Rock incorporates electric guitars, usually grouped with a bass guitar, drums, and one or more singers. Typically, rock music is based on a 4/4 time signature using a verse–chorus form, but the genre and its branches has become extremely diverse. Lyrics of rock music often tell stories of romantic love, but also address social or political themes.