The duration of the contract is very important, as the writer cannot sell songs to any other entity during this time. Length of the contract will be discussed before the contract is written. Musical composition can refer to an original piece of music, either a song or an instrumental music piece, the structure of a musical piece, or the process of creating or writing a new song or piece of music. The word "song" is widely misused by people in the popular music industry to describe any musical composition, whether sung or played only by instruments. People who create new compositions are called composers in classical music. In popular music and traditional music, the creators of new songs are usually called songwriters; with songs, the person who writes new words for a song is the lyricist. The task of adapting a composition for different musical ensembles is called arranging or orchestration, may be undertaken by the composer or separately by an arranger based on the composer's core composition. A composition may have multiple arrangements based on such factors as intended audience type and breadth, musical genre or stylistic treatment, recorded or live performance considerations, available musicians and instruments, commercial goals and economic constraints. If it is not deemed work for hire under federal copyright law, then all rights are transferred to the producer. In some cases, a pop or traditional songwriter may not use written notation at all, and instead compose the song in their mind and then play, sing and/or record it from memory. In jazz and popular music, notable sound recordings by influential performers are given the weight that written or printed scores play in classical music.