Ice sheet, ice shelf and iceberg কী?

An ice sheet is a mass of ice covering more than $50\,000\,\mathrm{km}^{2}$ of land, like a huge dome that spreads outwards in all directions. Where ice flowing off the land reaches the sea and goes on floating on it, still joined to the ice behind it, it forms an ice shelf. An iceberg is a large block of ice, more than $5\,\mathrm{m}$ across, that has broken off a glacier or an ice shelf and floats in the sea.