Rock music is a broad genre of popular music, originating as “rock and roll” in the United States in the early 1950s. Rock developed into many different styles in the 1960s onward, mainly in the UK and United States. Musically, rock centers on the electric guitar, usually as part of a band with electric bass, drums, and singers. Typically, rock has a 4/4 time signature and a verse-chorus format, but the genre can be extremely diverse. Lyrics in rock often discuss romantic love but also address other themes commonly social or political. In the late 1960s, many subgenres emerged from rock: blues rock, folk rock, country rock, and jazz-rock. These types of rock music later contributed to the development of psychedelic rock. Then came progressive rock, glam rock, and heavy metal. In the late 1970s, punk rock produced energetic social and political criticisms, and it was an influence in 1980s new wave, post-punk and alternative rock. In the 1990s, alternative rock dominated mainstream in the form of grunge, Britpop, and indie rock. From then on, other subgenres emerged, like pop punk, rap rock, and rap metal, as well as attempts to revisit rock's early history at the beginning of the 2000s. Rock music serves as a statement for cultural and social movements, as well as an expression of youth revult against adult consumerism and conformity.