What does "folksonomy" mean?

Folksonomy is a word formed from a combination of "folk" and "taxonomy". It's a recently developed concept of the general public categorizing information according to what's most useful for the masses, and is considered in opposition to the sometimes more formal classification systems created by an entity such as the Library of Congress or Yahoo!. Folksonomies are often implemented using tags. An advantage of tags over a hierarchical taxonomy is that it's easy to apply multiple tags to a single item, rather than having to decide which category to place the item in.