The Conditions of Readiness:
The legendary guru of the combat 1911, Jeff Cooper, came up with the "Condition" system to define the state of readiness of the 1911-pattern pistol. The are:
Condition 0 - A round is in the chamber, hammer is cocked, and the safety is off.
Condition 1 - Also known as "cocked and locked," means a round is in the chamber, the hammer is cocked, and the manual thumb safety on the side of the frame is applied.
Condition 2 - A round is in the chamber and the hammer is down.
Condition 3 - The chamber is empty and hammer is down with a charged magazine in the gun.
Condition 4 - The chamber is empty, hammer is down and no magazine is in the gun.
The mode of readiness preferred by the experts is Condition One. Generally speaking, Condition One offers the best balance of readiness and safety. Its biggest drawback is that it looks scary to [firearm function ignorant] people who don't understand the operation and safety features of the [or any] pistol
Source - http://www.sightm1911.com/Care/1911_conditions.htm