Another classification used by scientists to describe sea ice is based on age, that is, on its development stages. These stages are: new ice, nilas, young ice, first-year and old.

New ice is a general term used for recently frozen sea water that does not yet make up solid ice.

First-year sea ice is ice that is thicker than young ice but has no more than one year growth.

Old sea ice is sea ice that has survived at least one melting season (i.e. one summer), up to 3 meters (10 feet) or more. For this reason, this ice is generally thicker than first-year sea ice.

Old ice is commonly divided into two types: second-year ice, which has survived one melting season and multiyear ice, which has survived more than one. (In some sources, old ice is more than 2-years old.)

Multi-year ice is much more common in the Arctic than it is in the Antarctic. The reason for this is that sea ice in the south drifts into warmer waters where it melts. In the Arctic, much of the sea ice is land-locked.

More Info: en.wikipedia.org