the.com/cover crop

means A crop planted not to be sold or eaten but to protect and enrich the soil—holding it against erosion, smothering weeds, and feeding nutrients back into the ground.

from Straightforward agricultural English: 'cover' because it blankets and shields bare soil, 'crop' because it's sown and grown like any other. The term entered agricultural usage as farmers formalized soil-conservation and rotation practices, tracing partly to older traditions of planting clover, vetch, or rye between main harvests to rest the land—what was once called 'green manure' before 'cover crop' became the standard term.