Folksonomies in SharePoint 2010 Sites
A folksonomy is a taxonomy (or set of terms) that arises as a result of people applying their own tags (metadata) to content objects. SharePoint 2010 provides another kind of metadata, keywords, that you can use to apply free-form terms to content.
People use the tags that make sense to them, so over a period of time as more people tag, the folksonomy becomes more and more appropriate for the audience by associating content objects with the words and concepts people use to think about them.
Unlike metadata terms, keywords aren’t organized into a hierarchy that users select from. Instead, users can enter any value into a keyword field. SharePoint 2010 provides a Managed Keywords column that's configured already for use as a free-form keywords field.
The Managed Keywords field is a site column. The column uses a Managed Metadata column type that’s configured to use the site’s default keyword store. Each site needs to be configured with one default keyword store in an MMSA. The site can be associated with multiple instances of an MMSA, each with its own configuration settings, but only one can be designated as the default keyword store.
Enterprise Wikis use a Managed Keywords column. When someone enters a keyword with a Managed Keywords field, that value is available for everyone else to use.
Managed keywords provide a way to allow your users to enter their own free-form terms to a list item, document, or other library item. They’re a useful way to allow users to create a free-form taxonomy, or folksonomy, of your items. Social tags are a kind of keyword, but they're used to vote or rate items.
One of the benefits of going through all the trouble of using a hierarchy of terms to classify content is that you can use that same hierarchy to navigate to content.