The Collaborative International Dictionary of English v.0.48:

avant-garde \a*vant`-garde"\ ([.a]*v[aum]nt"-g[aum]rd`), a.
   1. Of, pertaining to, or belonging to the avant-garde.
      [PJC]

   2. Characterized by the use of experimental techniques;
      modern; daring; radical.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

avant-garde \a*vant`-garde"\ ([.a]*v[aum]nt"-g[aum]rd`), n. [F.
   avant before + E. guard, F. avant-garde. See Avaunt.]
   The most advanced group of people in any field of endeavor,
   especially in literary and artistic work, usually
   characterized by new ideas and experimental techniques.
   [PJC]

WordNet (r) 3.0 (2006):

avant-garde
    adj 1: radically new or original; "an avant-garde theater piece"
           [syn: avant-garde, daring]
    n 1: any creative group active in the innovation and application
         of new concepts and techniques in a given field (especially
         in the arts) [syn: avant-garde, vanguard, van, new
         wave]