SharePoint Managed Metadata Services

Managed metadata is a hierarchical collection of centrally managed terms that you can define, and then use as attributes for items in Microsoft SharePoint. Managed Metadata Services will provide enterprise management of metadata terms and content types. This will allow organizations to share metadata taxonomies and terms across multiple SharePoint webs and site collections.
It allows content types to be shared across webs and site collections using the same service. This will provide a much more unified view of data across the organization. Different departments or groups may have their own site collections for managing their SharePoint application, but everyone in the organization can be using common content types and metadata.
This will make unified search and retention across the organization much simpler as common terms can be used to search from data across the enterprise.

Taxonomy

A taxonomy is a formal classification system. A taxonomy groups the words, labels, and terms that describe something, and then arranges the groups into a hierarchy.
Organizations create taxonomies in too many ways to list. They create Chart of Accounts taxonomies to manage accounting systems, organization charts and job classifications to manage employees, product catalogs and so on. All these taxonomies are structured hierarchies of information; formal classification systems that help people handle information.

Folksonomy

A folksonomy is an informal classification system. It is evolves gradually as web site users collaborate on words, labels, and terms to content on a sit.

Go to Central Administration -> Application Management -> Manage metadata Service applications

Managed Metadata Hierarchy