A safety lock, or simply the safety, was a device that prevented a weapon from accidentally discharging and causing injury.
In 2269, Spock questioned what the null setting on the Slaver weapon was for, as it did not appear to be a safety lock. (TAS: "The Slaver Weapon")
In order to manually launch a quantum torpedo aboard a starship, it was first required for them to have their safeties detached. (DS9: "For the Uniform")