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Rock music is a form of popular music with a prominent vocal melody, accompanied by guitar, drums, and bass. Many styles of rock music also use keyboard instruments such as organ, piano, mellotron, and synthesizers. Other instruments sometimes utilized in rock include saxophone, harmonica, violin, flute, French horn, banjo, melodica, and timpani. Also, less common stringed instruments such as mandolin and sitar are used. Rock music usually has a strong back beat, and often revolves around the guitar, either solid electric, hollow electric, or acoustic.

Rock music has its roots in 1940s and 1950s rock and roll and rockabilly, which evolved from blues, country music and other influences. According to the All Music Guide, "In its purest form, Rock & Roll has three chords, a strong, insistent back beat, and a catchy melody. Early rock & roll drew from a variety of sources, primarily blues, R&B, and country, but also gospel, traditional pop, jazz, and folk. All of these influences combined in a simple, blues-based song structure that was fast, danceable, and catchy."[1]

In the late 1960s, rock music was blended with folk music to create folk rock, blues to create blues-rock and with jazz, to create jazz-rock fusion, and without a time signature to create psychedelic rock. In the 1970s, rock incorporated influences from soul, funk, and latin music. Also in the 1970s, rock developed a number of subgenres, such as soft rock, heavy metal, hard rock, progressive rock, and punk rock. Rock subgenres that emerged in the 1980s included synthpop, hardcore punk and alternative rock. In the 1990s, rock subgenres included grunge, Britpop, indie rock, and nu metal.

A group of musicians specializing in rock music is called a rock band or rock group. Many rock groups consist of a guitarist, lead singer, bass guitarist, and drummer, forming a quartet. Some groups omit one or more of these roles and/or utilize a lead singer who plays an instrument while singing, forming a trio or duo; others include additional musicians such as one or two rhythm guitarists and/or a keyboardist. More rarely, groups also utilize stringed instruments such as violins or cellos, and/or horns like saxophones, trumpets or trombones.

Post-punk
Main article: Post-punk
Alongside New Wave, post-punk developed as an outgrowth of punk rock. In a way was tied to punk rock. Sometimes thought of as interchangeable with New Wave, post-punk was typically more challenging, arty, and abrasive. The movement was effectively started by the debut of Public Image Ltd. in 1978, formed by former Sex Pistols singer John Lydon (formerly Johnny Rotten), and was soon joined by bands such as Joy Division, Siouxsie & the Banshees, The Fall, Gang of Four, and Echo & the Bunnymen. Predominantly a British phenomenon, the genre continued into the 1980s with some commercial exposure domestically and overseas, but the most successful band to emerge from post-punk was Ireland's U2, which by the late 1980s had become one of the biggest bands in the world.

Pop punk
Main article: Pop punk
One result of the 70s punk explosion was pop punk. Championed by bands such as the Buzzcocks and the Ramones, the genre was never as commercially successful as the name may have suggested, but its influence can be still be heard in many artists today; the fusion of pop melodies, rapid-fire playing of instruments, and the raw and visceral lyrics and sound of punk rock is apparent in everyone from Nirvana to Oasis.

Today, pop punk is used to describe modern rock bands with a heavy pop influence such as Green Day, Rancid, The Offspring and NOFX are common examples of the sub-genre, while Blink-182 and Sum 41 brought the sub-genre to new commercial heights in the late nineties to early 2000s

Emo
In the early 2000s, pop punk began to regain popularity. Media institutions began to label this scene as emo despite the fact that emo was originally an underground offshoot of 80s hardcore rock, involving such bands as Sunny Day Real Estate. There is still a lot of debate over which bands truly are emo, and the term could be used to describe everything including Fugazi. As the name suggests, the lyrics in many emo songs are often about depression and troubled relationships. Recently dubbed emo bands include: 30 Seconds To Mars, My Chemical Romance,[5] Fall Out Boy,[6] Cute Is What We Aim For[7] The Used and Panic at the Disco.[