Big Bang Theory Definition

A scientific theory describing the origin of all space, time, matter, and energy approximately 13.7 billion years ago from the violent expansion of a singular point of extremely high density and temperature.
American Heritage
A theory of cosmology holding that the expansion of the universe began with a gigantic explosion (big bang) between 12 and 14 billion years ago.
Webster's New World
The big bang theory is defined as the theory that the universe may have been created in a huge explosion at least 12 billion years ago, or is a successful comedy series created by Chuck Lorre in 2007 about four geeky scientists and a waitress neighbor.
An example of the big bang theory is the accepted scientific theory that the universe started when a hot dense state expanded and exploded causing the universe to cool and start to convert energy into its current state.