The Collaborative International Dictionary of English v.0.48:

Unemployment \Un`em*ploy"ment\, n.
   Quality or state of being not employed; -- used esp. in
   economics, of the condition of various social classes when
   temporarily thrown out of employment, as those engaged for
   short periods, those whose trade is decaying, and those least
   competent.

   Note: Unemployment is usually cointed as the condition of
         those who wish to work, but cannot find a suitable job,
         rather than others who may voluntarily refrain from
         working, such as retired persons, youth, or those
         remaining at home to care for young children. The

   unemployment rate in economics is thus the proportion of
      those actively seeking work but unable to find it, to the
      total labor force, expressed as a percentage.
      [Webster 1913 Suppl. +PJC]

WordNet (r) 3.0 (2006):

unemployment rate
    n 1: the percentage of the work force that is unemployed at any
         given date