An ice cap is a mass of ice that covers less than 50,000 square kilometers of land area. Larger ice masses are termed ice sheets. Ice caps are not constrained by topography and they can lie over the tops of mountains. They are technically a type of glacier, which is a broader category of flowing ice and which can be much larger and more mobile than ice caps.
Ice caps and other types of glaciers form at higher elevations because the air is thinner there than at lower elevations and thus less able to retain heat, thereby allowing snow to remain unmelted and accumulate. What are commonly referred to as the polar ice caps are not strictly ice caps because they greatly exceed the 50,000 square kilometers limit. The world's largest ice cap is probably the Severny Island ice cap in the Russian Arctic, which measures roughly 20,500 square kilometers and covers about 40 percent of the island.