What is Billet?

Legal Definition
A billet is a term for living quarters to which a soldier is assigned to sleep. Historically, it referred to a private dwelling that was required to accept the soldier.

Soldiers are generally billeted in barracks or garrisons when not on combat duty, although in some armies soldiers with families are permitted to maintain a home off-post. Used for a building, the term is more commonly used in British English; United States standard terms are quarters, barracks, "Single (Soldier) Housing" or "Family Housing".
-- Wikipedia
Legal Definition
A soldier's quarters in a civilian's house; or the ticket which authorizes him to occupy them. In French law. A bill or promissory note. Billet a ordre, a bill payable to order. Billet a vue, a bill payable at sight. Billet de complaisance, an accommodation blll. Billet de change, an engagement to give, at a future time, a bill of exchange, which the party is not at the time prepared to give. Story, Bills, ยง 2, n.
-- Black's Law Dictionary