The phrase "to power off" means to turn off or disconnect a device, system or machine from its source of electrical power. This can be done by either unplugging the device, turning off an electrical switch, or pressing and holding the power button on electronic devices such as smartphones, laptops, and tablets until they enter sleep mode. Powering off is often necessary when a machine needs to be restarted, repaired, maintained or updated, or when it's no longer in use.