The Collaborative International Dictionary of English v.0.48:

Hertz \Hertz\, n. [from the German physicist Heinrich Hertz.]
   a unit of frequency equal to one cycle per second; it is
   abbreviated Hz. It is commonly used to specify the frequency
   of radio waves, and also the clock frequencies in digital
   computers. For these applications, kilohertz and megahertz
   are the most commonly used units, derived from hertz.
   [PJC]

WordNet (r) 3.0 (2006):

hertz
    n 1: the unit of frequency; one hertz has a periodic interval of
         one second [syn: hertz, Hz, cycle per second,
         cycles/second, cps, cycle]
    2: German physicist who was the first to produce electromagnetic
       waves artificially (1857-1894) [syn: Hertz, Heinrich
       Hertz, Heinrich Rudolph Hertz]
    3: German physicist who with James Franck proved the existence
       of the stationary energy states postulated by Bohr
       (1887-1975) [syn: Hertz, Gustav Hertz, Gustav Ludwig
       Hertz]