What is a "Seneschal"? In medieval times, the Seneschal was the steward of a Great House. Seneschals also performed duties similar to a governor or other administrative or judicial officer.
In the SCA, a Seneschal is like the city manager to the Baron and Baroness, who are similar to a city mayor. The Seneschal helps facility the legal aspects of running events, membership, and the general business of the barony.