From AMS Glossary
A mass of land ice, formed by the further recrystallization of firn, flowing continuously from higher to lower elevations.
This term covers all such ice accumulations from the extensive continental glacier to tiny snowdrift glaciers. Nearly all glaciers are classified according to the topographical features with which they are associated, for example, highland glacier, plateau glacier, piedmont glacier, valley glacier, cirque glacier. They are also classified according to their seasonal temperatures, or melting characteristics, as temperate glaciers or polar glaciers. If a glacier is flowing, it is active or living; but an active glacier may be advancing or retreating depending upon the rate of flow compared to the rate of ablation at the terminus. A glacier that has ceased to flow is termed stagnant or dead.