1. The process of fossilizing a plant or animal that existed in some earlier age.
2. The process of being turned to stone.
3. Becoming inflexible or out of date.

Fossilization is considered a rare occurrence because most components of formerly-living things tend to decompose relatively quickly following death.

In order for an organism to be fossilized, the remains normally need to be covered by sediment as soon as possible; however, there are exceptions as to when an organism becomes frozen, desiccated, or comes to rest in an anoxic (oxygen-free) environment; such as, at the bottom of a lake.