Singing is the act of producing musical sounds with the voice, and augments regular speech by the use of both tonality and rhythm. A person who sings is called a singer or vocalist. Singers perform music known as songs that can either be sung a cappella (without accompaniment) or accompanied by musicians and instruments ranging from a single instrumentalist to a full symphony orchestra or big band. Singing is often done in a group of other musicians, such as in a choir of singers with different voice ranges, or in an ensemble with instrumentalists, such as a rock group or baroque ensemble.

Singing can be informal and done for pleasure; for example, singing in the shower or karaoke; or it can be very formal, as in the case of singing during a religious ritual such as a Mass or professional singing performances done on stage or in a recording studio. Singing at a high amateur or professional level usually requires instruction, and regular practice.^[1] Professional singers usually build their careers around one specific musical genre, such as Classical or rock, they typically take voice training provided by a voice teacher or vocal coach throughout their career.

source: http://en.wikipedia.org