Icebergs are large pieces of frozen freshwater that have broken off from a glacier or ice shelf and now float on the surface of an ocean. Icebergs can be hazardous to sea-going ships and may be one reason a particular section of sea is treacherous. Fictional icebergs often have strange things frozen within them – leviathans, creatures or people from a lost age, alien spaceships, or other elements. If the iceberg is sufficiently large, a fictional iceberg may more closely resemble an island or frozen region. In that case there may be structures such as ruins, fishing shacks, research stations, or shipwrecks on the surface. Icebergs are home to penguins, polar bears, and lost adventurers.

Fictional (and real) icebergs are a variety of shapes. Tabular icebergs are flat on top with steep sides resembling a plateau. The largest icebergs, those more akin to ice islands, are often this shape. Other types of icebergs have pinnacles, are domed, or in the shape of wedges. Some icebergs feature channels of water that flow across them, causing them to appear as separate sections of ice connected under the surface.

As icebergs are chunks of ice that have broken off from an ice shelf or glacier, they are an opportunity for worldbuilders to explore what structures, people, or creatures became trapped on a now floating mass.