Which term refers to land that is inactive or unproductive?

The term "fallow" specifically describes land that has been plowed and tilled but is intentionally left unseeded or uncultivated for a period of time. This practice is often used to allow the land to recover its nutrients, making it more productive in future cropping seasons. A fallow period is vital for sustainable agriculture, ensuring that soil health is maintained and avoiding the depletion of essential nutrients.

In contrast, the other terms do not convey the same meaning. "Imperious" refers to something that is commanding or dominant, which is unrelated to land use. "Extant" describes something that still exists or is in existence, often used in biological contexts to refer to species that are still alive, rather than land conditions. "Idyll" relates to a simple and peaceful scene or experience, often in a pastoral sense, and does not specifically denote land condition or productivity. Hence, fallow is the appropriate choice for describing land that is inactive or unproductive.