What does theme mean in music terms?

In music, a theme is a distinctive melody or musical idea that unifies a composition or movement. It is often the main component of a theme and variations movement form, and is typically repeated and developed throughout a piece. A theme can be played by any instrument or group of instruments, and can vary in length and complexity. It can also be used as the basis for other types of musical forms, such as the sonata form and the rondo form.