A musical instrument is an object or device that is used to produce musical sounds. Musical instruments have been in use for tens of thousands of years, but the variety and capabilities have increased greatly during the past several hundred as a result of technological advances in materials, structures and construction techniques as well as due to the ever-increasing demands by performers and audiences.
There are various systems of classification of musical instruments, but the most commonly used is the means by which they produce music. The dominant system today, which actually dates back to ancient Greece, divides instruments into the three broad categories of wind, strings and percussion. However, many instruments do not fit neatly into this scheme. For example, the piano has strings, but they are struck by hammers, and thus it has characteristics of both a string instrument and a percussion instrument. Also, this scheme does not include instruments which produce their sound electronically, such as the theremin and synthesizers.