Definition & Meaning of "jump the gun"

What is the origin of the idiom "jump the gun" and when to use it?

The idiom "jump the gun" has its origin in the sport of horse racing rather than track and field. In horse racing, a starting gun is used to signal the beginning of the race. The phrase "jump the gun" originally referred to a horse that began running before the starting signal was given, resulting in a false start. It is now commonly used when someone initiates an action or makes a judgment before the appropriate time, without having all the necessary information or considering the full consequences.