The Big Bang is the term which refers to the origin point of the universe, an instantaneous expansion of a microscopic singularity. It is believed to have been coined by a human astronomer in the 20th century.
While attempting to flee from his fellow Q, Quinn transported the USS Voyager to a point in time shortly after the Big Bang. (VOY: "Death Wish")
After his discovery of the Omega molecule, professor K'mtu Ketteract theorised that this molecule was the source of the Big Bang. (VOY: "The Omega Directive")