Any part of the earth's seasonal or perennial ice cover that has formed over land as the result, principally, of the freezing of precipitation; opposed to sea ice formed by the freezing of seawater. Thus, an iceberg or tabular iceberg is land ice as well as its parent glacier, ice sheet, or ice shelf. The two major concentrations of land ice are the ice sheets of Greenland and Antarctica. Glaciers and ice caps are the other important forms.