A tarn is a high lake resting in a hollow carved by glaciers, often beneath crags or steep mountain slopes. Its dark reflective water gives poets a natural mirror for cloud, moon, and inward thought. Because tarns are isolated and difficult to reach, they can seem untouched by ordinary time, though wind and rain continually disturb them. A poem may use a tarn to hold silence, hidden depth, and the lingering trace of ice in a living landscape.

A tarn is a small upland lake, particularly associated in British usage with mountainous areas such as the Lake District. Many occupy hollows shaped by glacial action, although everyday usage does not always follow a strict geological definition. In poetry, the word can establish a northern or mountainous setting and often suggests isolation, stillness, reflection, coldness, or dark depth. Weather may transform its mood dramatically. Related terms include corrie, cirque, lake, pool, mere, fell, glaciation, mountain landscape, reflection, solitude, and the sublime.