People who study medieval stuff generally recognize the Wife of Bath's Prologue as part of the "confessional" genre. In morality plays, in which various virtues and vices were personified by characters with names like Fortitude and Hope, or Lust and Greed, the evil characters would confess their sins as a way of teaching the audience about what those sins looked like. The Wife's Prologue definitely borrows that element of the "confession" scene – namely, any time she admits to morally questionable acts like lying and lust.
However, there are some problems with viewing the Wife's Prologue as totally confessional. For one thing, the Wife seems at certain points to be defending her lifestyle, particularly when she uses Biblical passages and life experience in support of remarriage. It's also unclear exactly which vice the Wife would represent. She's certainly sinful, but does she personify lust? Greed? Deceit?
The Wife of Bath's Prologue can't be called just autobiography either, because of the way it often veers away from straightforward narration of the Wife's history to argumentative, almost sermon-like passages. The Pardoner certainly recognizes this latter aspect of the Wife's Prologue when he exclaims to her, "Ye been a noble prechour in this cas!" (171). In fact, what's innovative about the Wife of Bath's Prologue is the way it blends all of these genres – confession, autobiography, and sermon – into one entertaining package.