1. To cease functioning or operating by disconnecting from a power source. To avoid damaging the screen, these new LED televisions power off automatically after half an hour if they are not being used. The hackers were able to rewrite the security system's code so that it powered off without sending an alert or raising an alarm.

2. To deactivate or shut down some electronic device, appliance, tool, or piece of machinery by causing or prompting it to disconnect from a power source. It's important to power off your computer completely each day to help it function properly. The dock worker powered his front loader off when he heard the alarm.