big bang

Short definition from Wiktionary

Noun

1. 1
   An explosion giving rise to a universe.
2. 2
   A large implementation of a system rather than phased or gradual delivery

Proper noun

1. 1
   The cosmic event that marks the beginning of time and the rapid expansion of space for the visible universe. The evolution of the universe since that beginning point is described by the Big Bang Theory.
2. 2
   The sudden deregulation of financial markets effected by prime minister Margaret Thatcher in 1986.