Biodegradable plastics are polymers that can decompose under the action of micro-organisms (bacteria, fungi), forming water, carbon dioxide (or methane) and biomass that is harmless to the environment.
Biodegradation can take place in a variety of environments (compost, soil, water, etc.), and will be more or less rapid depending on parameters such as temperature, humidity, the presence of micro-organisms and, of course, the nature of the polymer itself.
The biodegradability of a polymer is not linked to the resource with which it was produced, but solely to its chemical structure. There are biodegradable plastics made from both fossil and renewable resources.