@meena yeah, comes from Advocatus Diaboli (latin for Devil's Advocate), they were a canon lawyer that had the job of uncovering any character flaws or misrepresentation of evidence favouring the canonisation of a candidate

They served as the party advocating against making someone a saint, and were up against the Advocatus Dei (God's Advocate) who were arguing that someone should be made a saint

@meena yeah, it's meant to be for the sake of debate between people acting in good faith (pun not intended) but everyone knows how debates go on the internet