What is a Turn in the context of the Stronghold?

Some things in the Stronghold, such as taxes or resource generating buildings, depend on "turns". What is a turn in this context? How do I go from one turn to the next?

Near as I've observed so far, Stronghold "turns" are not tied to units of game time, but rather to the completion of quests (and possibly tasks, also). It's not clear if the completion of one quest/task produces an advancement of one turn, or if some quests cause more than one turn advancement (or perhaps each quest update causes a turn advancement).

Presumably they're implemented like this to avoid the possibility of resting over and over to generate effectively-infinite cashflow through tax collection.