The Collaborative International Dictionary of English v.0.48:

Treasury stock \Treas"ur*y stock\ (Finance)
   Issued stock of an incorporated company held by the company
   itself.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

treasury stock
    n 1: stock that has been bought back by the issuing corporation
         and is available for retirement or resale; it is issued but
         not outstanding; it cannot vote and pays no dividends [syn:
         treasury stock, treasury shares, reacquired stock]