Corrie – This is an arm chair shaped hollow found in the side of a mountain, e.g. Helvellyn, Lake District. They typically contain a lake, known as a tarn.
The video of Helvellyn below features a corrie containing a lake known as Red Tarn.
Arete – This is a narrow, knife edge ridge separating two corries, e.g. Striding Edge, Helvellyn.
The video below shows an arete in the Swiss Alps.
Pyramidal Peaks – These are formed when three or more corries form in the side of one mountain, e.g. The Matterhorn, Switzerland or Mount Snowdon, Snowdonia National Park, Wales.
Tarn – This is a lake found in a corrie, e.g. Red Tarn, The LakeDistrict.