Rock is a broad term that brings together a variety of musical genres. Its original form, known as rock and roll, arose mostly from the combination of two previous genres such as rhythm and blues and country. Rock music was also heavily nurtured from blues and folk, and incorporated influences from jazz, classical music and other sources. Rock has focused on electric guitar, usually as part of a rock band with singer, bass, drums and sometimes keyboard instruments such as organ and piano.
Thanks for the adition. :)