Iceberg
U.S. Geological Survey photo by Bruce Molnia (fair use policy)
Icebergs are part of a spectrum of floating ice. When glaciers reach water, whether it's a lake or the ocean, they break off in pieces. The smallest pieces are called brash ice (less than 2 meters across), and larger pieces are called growlers (less than 1 meter above the water) or bergy bits (up to 5 m above water or 10 m across). This chunk of ice is definitely an iceberg as it's about 100 m long and sticks 10 m above the waters of Portage Lake in Alaska.
Icebergs have about nine-tenths of their volume under water. Icebergs are not pure ice because they contain air bubbles, often under pressure, and also sediments. Some icebergs are so "dirty" that they carry significant amounts of sediment far out to sea. The great late-Pleistocene outpourings of icebergs known as Heinrich events were discovered because of the abundant layers of ice-rafted sediment they left across much of the North Atlantic seafloor.
Sea ice, which forms on the open water, has its own set of names based on various size ranges of ice floes.
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