The interlock of a Laser is a mechanism which can contribute to laser safety by automatically SWITCHING off the laser or by blocking a Laser Beam e.g. when a protective box or a door is opened. Commercial lasers often have interlock connections on the back side of the laser driver (i.e., the electronic controls); one can connect those e.g. to an electrical Contact which is installed at a door.
As interlocks can be very annoying in real life, they are often tampered with (which is often too easy to do). Therefore, one should not overestimate their usefulness for laser safety.