A seneschal is a trusted yeofolk who oversees the financial affairs of a Dawnish noble house. It is considered very poor form for a noble, especially the earl of a house, to concern themself with money - it distracts them from focusing on their house's glory, after all - and so the seneschal is always a yeofolk. Many seneschals are employed from the ranks of those yeofolk farmers who manage their farms particularly well, while others are merchants whose competence have caught their earl's eye.
The seneschal must ensure that the nobles of the house are solvent enough to arm and armour themselves, to go to war, and to throw banquets just as often as they want to. They must make sure that the noble house has a presence in the Imperial Bourse, and that its financial assets are not forgotten by relevant Senators and other important figures, even though the nobles of the house won't talk about them. They must oversee the entire house's assets, and ensure that it prospers; as such the seneschal can be one of the most powerful people in a noble house.
Playing a seneschal
Playing a seneschal should ensure you a busy game - when your earl gives an order to organise a tourney or a banquet, you need to know when, where, how much it will cost. You may have to skirt the edges of Dawnish tradition - or ignore it entirely - to achieve your goals, but you must always appear to have acted to further the glory of your house. More importantly, even when you're not being given orders, it is your job to make sure the house stays afloat, which may mean dealing with other seneschals, senators, foreigners, and the many and varied denizens of the Bourse.