a. It allows to define a hierarchical collection of centrally managed terms that can be used as attributes for items in Microsoft SharePoint Server
b. It allows content types to be shared across webs and site collections
c. It has a Term Store Management Tool that is an interface that can be used to define managed terms and enterprise keywords
d. It makes unified search and retention across the organization much simpler as common terms can be used to search from data across the enterprise.
e. All the above