The Free On-line Dictionary of Computing (19 January 2023):

power-on reset
POR

   (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.

   (2012-02-09)