1. Specifically, ice formed by the freezing of seawater; as opposed, principally, to land ice. In brief, it forms first as lolly ice (frazil crystals), thickens into sludge, and coagulates into sheet ice, pancake ice, or into floes of various shapes and sizes. Thereafter, sea ice may develop into pack ice and/or become a form of pressure ice. 2. Generally, any ice floating in the sea.