An idiophone is any musical instrument which creates sound primarily by way of the instrument itself vibrating, without the use of strings or membranes. It is one of the four main divisions in the original Hornbostel-Sachs scheme of musical instrument classification, the others being membranophone, chordophone and aerophone (a fifth division, electrophone, was added in a later revision).
Most percussion instruments which are not drums are idiophones. Hornbostel-Sachs divides idiophones into four main sub-categories, with the first division, struck idiophones, containing most of the non-drum percussion instruments familiar in the west. They include all idiophones which are made to vibrate by being hit, either directly with a stick or hand (like the triangle or marimba), or indirectly, by way of a scraping or shaking motion (like maracas). Various types of bells fall into both categories.
The other three sub-divisions are rarer. They are plucked idiophones, such as the jew’s harp, music box or mbira (thumb piano); blown idiophones, of which there are a very small number of examples, the Aeolsklavier being one; and friction idiophones, such as the glass harmonica, daxophone, styrophone, musical saw, or nail violin (a number of pieces of metal or wood rubbed with a bow). A number of idiophones that are normally struck, such as vibraphone bars and cymbals, can also be bowed.