noun
imperial villa
A residence used by the Japanese imperial family, typically a secondary or vacation home.
那須御用邸は皇室の静養地として知られている。
The Nasu Imperial Villa is known as a retreat for the imperial family.
離宮 is a detached palace, often larger and more formal than 御用邸, which is typically a villa or retreat.
御 (honorific prefix) + 用 (business, use) + 邸 (residence). The term refers to a residence for the imperial family's use.