A "Billet-doux" is a love letter. (Sweet card, or sweet ticket) Also the name of a tune by Django Reinhardt & Stephane Grappelli.
But...
"Billet-Deux" is the name of a modern gypsy jazz combo....
A billet was an assigned place to sleep on base, usually in a barracks or onboard a ship. The British commonly billeted soldiers in the homes of the colonists. Off base, they have tents if they even...