In its most basic form, a song is poetry set to music. It combines melody and vocals, and is often written in verse (often containing the words of the song) with a refrain or a riff in between each line of the verse. Some songs, like the rhyming poems of Pablo Neruda, have no words at all but just a melodic sound that conveys emotion and mood.
A song may also be an instrumental work, such as a piece of classical music, or a musical theater song. It can also be found in film and television, and within operas, plays, and other stage shows of any kind. In the case of film and television, a song may be recorded on audio or video (or both).
Some musicians write and record songs to make money. Others, such as folk singers, write and sing traditional songs as part of a culture. Many musicians create parodies of other artists’ songs, changing the lyrics but keeping the same melody (often known as a hook), to criticize or ridicule the original artist and song. The art of songwriting is highly varied and can be very difficult to master.
In general, the word “song” can be applied to any type of musical composition that features a melody and lyrics or vocals. However, the term can be confusing because it may refer to a specific type of musical genre, such as an aria or recitative in an opera, a movement of a symphony, or the Kyrie of a mass. In those cases, it is best to use the word “piece” rather than “song,” or, if possible, the name of the work itself.