A keyboard instrument is a musical instrument played using a keyboard. The most common of these is the piano. Some other types of keyboard instruments include celestas, which are struck idiophones operated by a keyboard, carillons, which are highly different instruments that are usually housed in bell towers or belfries of churches or other municipalbuildings, and other non-acoustic instruments, such as various electronic organs, synthesizers, and keyboards designed to imitate the sound of other musical sounds.