It is a contrast to the term outcrop, if not a perfect antonym.
If rocks exposed at the present-day erosion surface are referred to as outcrops, then now-buried rocks that were exposed at ancient erosion surfaces are referred to as subcrops.
If part of a geological formation is close to the surface, it is a subcrop.
A subcrop is not outcropping, and is usually under the soil profile or alluvial sediments.
This article about a specific stratigraphic formation is a stub.