A composer is a person who writes music. The term refers particularly to someone who writes music in some type of musical notation; thus, allowing others to perform the music. This distinguishes the composer from a musician who improvises or plays an instrument.
The level of distinction between composers and other musicians also varies, which affects issues such as copyright and the deference given to individual interpretations of a particular piece of music. For example, in the development of classical music in Europe, the function of composing music initially had no greater importance than the function of performing music. The preservation of individual compositions received little attention, and musicians generally had no qualms about modifying compositions for performance. Over time, however, the written notation of the composer has come to be treated as strict instructions, from which performers should not deviate without good reason. Performers do, however, play the music and interpret it in a way that is all their own.
The term 'composer' is often used specifically to mean a composer in the Western tradition of classical music. In popular and folk music, the composer is typically called a songwriter (since the music generally takes the form of a song.)