An auto-da-fé (also auto da fé and auto de fe) was the ritual of public penance of condemned heretics and apostates that took place when the Spanish Inquisition or the Portuguese Inquisition had decided their punishment, followed by the execution by the civil authorities of the sentences imposed. Both auto de fe in medieval Spanish and auto da fé in Portuguese mean "act of faith".
The most extreme punishment imposed on those convicted was execution by burning. As the execution was more memorable than the penance which preceded it, in popular use the term auto-da-fé came to mean the punishment rather than the penance.
Read more about Auto-da-fé: History, In Popular Culture