Sea ice of not more than one winter's growth, developing from young ice; 30 centimetres or greater. It may be subdivided into thin first-year ice - sometimes referred to as white ice -, medium first-year ice and thick first-year ice.
Environment and Climate Change - Canada https://www.ec.gc.ca/glaces-ice/default.asp?lang=En&n=2CE448E2%E2%80%931&offset=4&toc=hide