In contrast to a taxonomy, which can be roughly translated as “classification management”, a folksonomy is a classification scheme that uses a crowd rather than experts to parse content. The idea of a folksonomy is closely related to tagging, which has enjoyed great vogue in online circles since 2005 at least.
The word folksonomy is a combination of folks, meaning "people", and -onomy, meaning "management". Literally, this can be taken to mean “management by people” and has nothing to do with classification – which comes from the prefix tax- – but the meaning is usually easy to intuit from context. It is also a relatively new word, so it usually comes with a definition when mentioned in text.
Tagging is exemplified by the social bookmarking service del.ic.ious, which originally started out as a part-time project by a single person, but was quickly acquired by Yahoo for 60 million US dollars (USD). Del.ic.ious lets you tag any webpage you visit with relevant words to describe its content. Anyone can view webpages corresponding to a specific tag or view which tags a given page has received. This tagging concept is synonymous with the phrase metadata and has been discussed for decades, but has never really caught on until the advent of del.ic.ious.
The tagging service Technorati lets users do the same thing with blog posts. Because these are supplied by the poster rather than unbiased visitors, technorati tags don’t always accurately reflect the content of the post, but 99.9% of the time, they do. Technorati tags are extremely popular, and today a substantial portion of all bloggers use them. Graphs of tagging frequencies let us peek into the mass consciousness – sometimes called the zeitgeist – for example, we saw a huge spike in instances of the “Katrina” tag following the hurricane of the same name.
A visual representation of a folksonomy is the tagcloud – a sequence of words of different sizes that represent popular tags by showing them in a larger font type. Tagclouds can be constrained in different ways: for example, anyone who tags will accumulate a personal tagcloud that reflects how frequently they use any given tag. A community can create a tagcloud describing its interests by merging the personal tagclouds of its members. Top-level tagclouds are created by sites like del.ic.ious when they compile tagclouds showing their most popular tags in any given time period, such as the previous week, in a glance.
WiseGEEK founder Denis Grosz came up with a variant on the tagging idea called nesstags when he suggested a scheme to add numbers to tags to describe how intense or prototypical an example of a tag the thing is. For example, we could tag photos of objects based on how much “purple-ness” they contain. A very purple thing might be tagged “purple9”, while something only slightly purple would be “purple2”. This could give rise to a much more sophisticated folksonomy.
Because tagging and the folksonomy concept are in style right now, they are often used in marketing to generate hype, and should accordingly be taken with a grain of salt. The term folksonomy was originally coined by the information architect Thomas Vander Wal.