What is the decocking lever in a semiautomatic pistol?

Often with a semiautomatic pistol, once a loaded magazine is inserted and the slide racked, you now have a pistol that is ready to fire: there is a fresh round in the chamber, the hammer (or striker) is cocked. This CAN be a dangerous situation, if the shooter isn't going to fire the weapon immediately.

In the past, a person would have to CAREFULLY lower the hammer while pointing the pistol in a safe direction. If they slipped, they would fire a bullet accidentally AND their thumb would get hurt--mashed by the recoiling slide & hammer.

A decocking lever prevents such accidents by LOWERING the cocked hammer to a safe position. Once utilized, if the shooter wanted to prepare the pistol for firing, they would have to:

Manually recock the hammer, if the pistol were a single action only type, or, manually recock, or utilize the pistol's long Double Action trigger, if the pistol was a Double Action/Single Action type.