In music a singer or vocalist is a type of musician who sings, i.e. uses the voice as an instrument to make music. A lead singer is one who sings the primary vocals of a song, as opposed to a backup singer who sings backup vocals to a song or harmonies to the lead singer.
In classical music and in opera, voices are treated just like musical instruments, thus special careers were developed out of each principal pitch.
Voices are commonly classified by sex and vocal range as follows: