Rock music is a genre of popular music that originated in the 1950s and has since evolved to include a wide range of sub-genres. At its core, rock music is characterized by its use of amplified electric instruments, particularly the guitar, bass, and drums, as well as its strong backbeat and emphasis on rhythm. Rock music typically features a vocal melody that is accompanied by guitar-based instrumentation, and its lyrics often address a wide range of themes, such as love, social issues, and the human experience. Rock music has been known to be diverse and it has been constantly evolving. Some of the popular sub-genres of rock music include classic rock, heavy metal, punk rock, alternative rock, and indie rock.