Rock is a broad genre of popular music that originated as 'rock and roll' in the United States in the late 1940s and early 1950s. It is characterized by a strong rhythm, simple melodies, and often revolves around the electric guitar, bass guitar, and drums. Over the decades, rock music has evolved into various subgenres, including hard rock, punk rock, and alternative rock, among others. The genre is known for its energetic performances and has been a major influence on culture, fashion, and attitudes. Rock music often addresses themes of rebellion, love, and social issues, and has been associated with movements for change and freedom throughout its history.