Singing was the act of using one's voice to create sounds or words as a form of music. One who sings was called a singer, while several individuals singing together may be known as a sing-along. A genre of film and play in which the performers sang was known as a musical.
In 2259, the USS Enterprise transmitted music into a subspace fold, creating a quantum uncertainty field in which individuals sang and danced during moments of heightened emotion, as though they were in a musical. The field became tethered to the Enterprise, spreading to other Starfleet and Klingon starships before the crew were able to shatter the field. (SNW: "Subspace Rhapsody")
Upon hearing Worf's rendition of the Klingon opera Aktuh and Maylota in 2368, the fat Ferengi Omag, asked "What is that dreadful noise? It sounds like a Bardakian pronghorn moose." (TNG: "Unification I")