WordNet (r) 3.0 (2006):

GHz
    n 1: 1,000,000,000 periods per second [syn: gigahertz, GHz,
         gigacycle per second, gigacycle, Gc]

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

GigaHertz
GHz

    (GHz) Billions of cycles per second.

   The unit of frequency used to measure the clock rate of
   modern digital logic, including microprocessors.

   (2001-05-14)