Condition 0 - A round is in the chamber, the hammer is cocked, and the safety is off.
Condition 1 - Also called "cocked and locked", this means that a round is in the chamber, the hammer is cocked, and the manual thumb safety is on.
Condition 2 - A round is in the chamber, the hammer is uncocked.
Condition 3 - There is no round in the chamber, the hammer is uncocked but a fully loaded magazine is inserted in the mag well.
Condition 4 - The chamber is empty, the hammer is uncocked and there is no magazine inserted in the mag well
A Glock with 1 in the chamber would fall under Condition 0 right? I prefer cocked and locked or Condition 1 via a 1911 or HK USP V1. My Kahr PM9 is like Condition 2. It requires a relatively long and heavish (6lbs or so) pull. I feel perfectly safe with my PM9. Condition 3 and 4... you might as well not even carry.