A sharp line on a hillside marking the boundary between well-vegetated terrain that has remained ice-free for a considerable time and poorly vegetated terrain that until relatively recently lay under glacier ice. In many areas the most prominent trim-lines date from the Little Ice Age (q.v.).

Trim-line (arrowed) dating from the Little Ice Age (c. 1750 to 1850), along the flanks of Grosser Aletschgletscher, Switzerland. Photo J. Alean.