Composer, Composer

The level of distinction between composers and other musicians varies, which affects issues such as copyright and the deference given to individual interpretations of a particular piece of music. In the development of European music, the function of composing music initially had no greater importance than that of performing it.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. In fact, in the concerto form, the soloist would often compose and perform a cadenza as a way to express their individual interpretation of the piece.

In popular and folk music, the composer is typically called a songwriter (since the music generally takes the form of a song).

Source: Wikipedia > Composer