What is Vidame?

Legal Definition
Vidame, a French term descended from mediaeval Latin vicedominus ('vice-lord', which may mean 'vice-count', depending on the feudal status of the territory), was a feudal title in France. The vidame was originally, like the avoué (advocatus), the royal or crown judge, a secular official chosen by the bishop of the diocese, with the consent of the count, to perform functions on-behalf of the prince-count in the church's earthly interest, canonically incompatible with the clerical state, or at least deemed inappropriate, especially involving violence, even in the service of justice, and to act as protector, rather in the tradition of the Roman Defensores.

Unlike the advocate, however, the vice-dominus was at the outset an ecclesiastic, who acted as the bishop's lieutenant (locum tenens) or vicar. But the causes that changed the character of the advocatus operated also in the case of the vidame.
-- Wikipedia
Legal Definition
In French feudal law. Originally, an officer who represented the bishop as the viscount did the count In process of time, these dignitaries erected their offices into fiefs, and became feudal nobles, such as the vidame of Chartres, Rheims, etc., continuing to take their titles from the seat of the bishop whom they represented, although the lands held by virtue of their fiefs might be situated elsewhere. Brande; Burrill.
-- Black's Law Dictionary