Glaciers are masses of land ice, formed by the further recrystallization of firn, flowing continuously from higher to lower elevations. Ice sheets are a continuous sheet of land ice that covers a very large area and moves outward in many directions. This type of ice mass is so thick as to mask the land surface contours, in contrast to the smaller and thinner highland ice. The continental glacier of Greenland is sometimes called the Inland Ice. This term is often used to describe the great ice masses that characterized the ice ages.
Definition source: United States Geological Survey
