Rock is a form of popular music, usually featuring vocals (often with vocal harmony), electric guitars, and a strong back beat; other instruments, such as the saxophone, are common in some styles. The genre of rock is broad, and its boundaries loosely-defined, with distantly related genres sometimes included. Pop music, in popular and contemporary parlance, is a sub-genre of popular music. Since the term spans many acts (rock, hip-hop, rhythm and blues (R&B), country, dance and operatic pop), it is reasonable to say that ‘pop music’ is a loosely defined category. The term is also used in a derogatory manner by those who feel that pop lacks any musically artistic meaning, or, for lack of better terminology, represents a ‘betrayal’ from the traditional sound of either the act itself or the specific genre to which the act belongs.