As the name suggests, a biodegradable item breaks down naturally and in the presence of microorganisms, fungi, or bacteria, will be ingested or dissolve back into the Earth, without leaving any solid trace behind. Such items are more desirable for our environment because they will eventually degrade back into nature and not add to our waste problem.
Items that are naturally biodegradable include wood, paper, cardboard, and food. On the other hand, many plastics are not biodegradable because they do not break down naturally and dissolve back into nature, and are therefore not considered biodegradable.
The term biodegradable should not be confused with the term compostable. All compostable items are biodegradable, but compostable items are specifically made to break down into compost, which can be used as an organically-rich fertilizer for plants.