Singing is the act of producing musical sounds with the voice. A person who sings is called a singer or vocalist (in jazz and popular music). Singers perform music (arias, recitatives, songs, etc.) that can sing with or without accompaniment by musical instruments. Singing is often done in an ensemble of musicians, such as a choir of singers or a band of instrumentalists. Singing can be formal or informal, arranged, or improvised. It may be done as a form of religious devotion, as a hobby, as a source of pleasure, comfort, or ritual as part of music education or as a profession.