NOUN (3)

1. the period of time during which a regent governs;

2. the period from 1811-1820 when the Prince of Wales was regent during George III's periods of insanity;

3. the office of a regent;

The Collaborative International Dictionary of English v.0.48:

Regency \Re"gen*cy\ (r?*jen*s?), n.; pl. Regencies (-s?z).
   [CF. F. r['e]gence, LL. regentia. See Regent, a.]
   1. The office of ruler; rule; authority; government.
      [1913 Webster]

   2. Especially, the office, jurisdiction, or dominion of a
      regent or vicarious ruler, or of a body of regents;
      deputed or vicarious government. --Sir W. Temple.
      [1913 Webster]

   3. A body of men intrusted with vicarious government; as, a
      regency constituted during a king's minority, absence from
      the kingdom, or other disability.
      [1913 Webster]

            A council or regency consisting of twelve persons.
                                                  --Lowth.
      [1913 Webster]

WordNet (r) 3.0 (2006):

regency
    n 1: the period of time during which a regent governs
    2: the period from 1811-1820 when the Prince of Wales was regent
       during George III's periods of insanity
    3: the office of a regent