Keyword Manager 

The Keyword Manager lets you create predefined or dynamically created keyword lists. You can use it to create system-wide lists, manage user-defined tags or just to categorise your content. 

Keywords are organised in hierarchies and can have one or more objects associated with them, such as a user, style, colour, files or components.
The Keyword Manager has the following features:

Flexible hierarchy structure - create keyword hierarchies with as many levels as you need and arrange them by dragging and dropping them in the right place.
Associate objects with keywords - use the chooser to select one or more objects you would like to associate with a keyword. This could be a blog entry with keywords as tags or a document with keywords that help to classify and categorise it in a document library.