When troops are sheltered under canvas (in tents), they are in camp.
When they are resting on the ground without tents (for instance, on the
firing line the night before or during a battle), they are in what is
called bivouac. When they occupy buildings in towns or villages, or huts
especially erected, they are in cantonment. When they are assigned to
public (such as post-offices, town halls, court houses, hotels, etc.) or
private buildings they are said to be billeted.