The Collaborative International Dictionary of English v.0.48:

auto-da-fe \auto-da-fe\, Auto-da-f'e \Au"to-da-f['e]"\, n.; pl.
   Autos-da-f['e]. [Pg., act of the faith; auto act, fr. L.
   actus + da of the + f['e] faith, fr. L. fides.]
   1. A judgment of the Inquisition in Spain and Portugal
      condemning or acquitting persons accused of religious
      offenses.
      [1913 Webster]

   2. An execution of such sentence, by the civil power, esp.
      the burning of a heretic. It was usually held on Sunday,
      and was made a great public solemnity by impressive forms
      and ceremonies.
      [1913 Webster]

   3. Hence: [Fig.] The public denunciation or punishment of a
      person who has offended the prevailing authorities.
      [PJC]

   4. A session of the court of Inquisition.
      [1913 Webster]

WordNet (r) 3.0 (2006):

auto-da-fe
    n 1: the burning to death of heretics (as during the Spanish
         Inquisition)