idle land; unused land; vacant land
Refers to land that is not being used for its intended purpose, often in economic or urban planning contexts.
The city announced a plan to turn idle land into a park.
There is a lot of unused land remaining in this area.
空地 simply means unused land in general, whereas 遊休地 specifically refers to land or facilities that are idle despite being intended for productive use.
Compound of 遊休 (idle, unused) and 地 (land). The exact historical derivation is uncertain, but the term is conventionally used in modern Japanese for idle or unused land.