house where the family is out; empty house
Refers to a house whose residents are temporarily away, leaving it unoccupied.
隣の家は留守宅で、夜になっても明かりがつかない。
The house next door is empty, and no lights come on even at night.
Compound of 留守 (るす, 'absence from home') and 宅 (たく, 'house').