A crag is a rough, jagged section of rock. Some sections of the Maine coast are made up of rugged crags and rocky beaches.
Steep rock faces and cliffs are covered with crags — if you're a rock climber, you might attempt to scale the crags of a jagged rocky mountain. Parts of northern England and Scotland are particularly famous for their crags, and in fact the root of the word crag is Celtic, related to the Old Irish crec, "rock," and the Welsh craig. "rock" or "stone."