The Collaborative International Dictionary of English v.0.48:

Extravaganza \Ex*trav`a*gan"za\, n. [Extravagance with an
   Italian ending: cf. It. stravaganza.]
   1. A composition, as in music, or in the drama, designed to
      produce effect by its wild irregularity; esp., a musical
      caricature.
      [1913 Webster]

   2. An extravagant flight of sentiment or language.
      [1913 Webster]

   3. a lavish or spectacular show or event, or presentation;
      as, Disney staged an extravaganza in Central Park that
      drew many thousands.
      [PJC]

WordNet (r) 3.0 (2006):

extravaganza
    n 1: any lavishly staged or spectacular entertainment