Sitecore Content Tree
One of the main concepts in Sitecore (and many other CMS systems) is the concept of the hierarchical content tree. The concept of hierarchy is an important form of metadata, allowing for a clear method of categorizing content.
Of course, there are issues and exceptions to this model - there are often cases where an item may belong in two places; are hiking boots camping gear, or footwear? Similarly, often a location in a hierarchy may have too many items to feasibly load and work with in a browser.
Sitecore is somewhat unique in that it allows icons to be set for each item in the tree. Properly used, this can also give an additional level of understanding for content authors to navigate and understand the information architecture of your site(s).