A songwriter is someone who writes the lyrics to songs, the musical composition or melody to songs, or both. That is to say, a songwriter is a lyricist, a composer, or both. The word 'songwriter' is however more commonly used to describe one who writes popular songs than to describe a writer of art songs.
History and background of songwriters
Songwriters may perform the songs they write themselves, or may write for somebody else to perform. People who sing their own songs are nowadays typically called singer-songwriters, although the tradition of doing this dates back hundreds of years. It is often speculated that pre-historic man must have made up and sung songs. More recently, the troubadours of the middle ages sang their own work, as did the German Minnesingers.