Definition - What does Lock Off mean?
Lock off is the process of turning off a machine and securing the switch in order that it cannot be turned back on without using a dedicated tool or a key. It is not simply turning a machine off with the possibility that someone could turn it back on while a person is working on it. Nor is it using an emergency stop switch. If the machine can be turned back on without using a special key or dedicated piece of equipment, it has not been locked off.
Safeopedia explains Lock Off
Lock off on most machines can be enacted by inserting a padlock through the main switch, so that it cannot be turned back on until the padlock is removed. If machines have multiple isolation switches, attempts should be made to integrate the systems so that there is only one lock off point. If this cannot be done, then the use of multiple switches must be incorporated into the lock off procedures. It is important that all copy keys of a lock are locked away.