Computer Dictionary of Information Technology

power-on reset

<hardware>(POR) The processes that take place when a hardware device is turned on. This may include running power-on self-test or reloading software from non-volatile storage. The term implies that the device has some reasonably complex internal state that will be set back to a "normal" initial condition. This state may include the physical state of the device (e.g. a printer) as well as data in the memory of an embedded system.

If a device has no reset button, and sometimes even if it does, turning it off and on again (power cycling) may be the only way to clear a fault.