A piece of rock that shows above the ground, where the solid rock underneath the soil comes up to the surface and can be seen. Picture a hillside of grass with grey stone breaking through it, or bare rock on a mountainside — that stone is an outcrop. It is a countable noun and belongs to geography, geology, hiking and nature writing; you would meet it in a textbook or a walking guide, not in conversation. It usually comes with 'of' and the kind of rock: an outcrop of granite, a limestone outcrop. There is also a verb, 'to outcrop', used by geologists to say that a layer of rock appears at the surface ('the coal seam outcrops near the river'), but that use is technical and rare. Geologists like outcrops because they are free windows into what is under the ground — you can read the layers without digging.