The Free On-line Dictionary of Computing (30 December 2018):

120 reset

    /wuhn-twen'tee ree'set/ (After 120 volts, US mains
   voltage) To cycle power on a computer in order to reset or
   unjam it.

   Compare Big Red Switch, power cycle.

   [Jargon File]

   (1994-11-23)