The Collaborative International Dictionary of English v.0.48:

ascot \ascot\ n. [from the fashionable clothjing worn at the
   Ascot races.]
   a cravat with wide square ends, tied so that the ends are
   laid flat; the ends are often secured with an ornamental pin;
   -- called cravat in Britain.
   [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

ascot
    n 1: a cravat with wide square ends; secured with an ornamental
         pin