From: http://www.hyperorg.com/backissues/joho-jul25-04.html#order

First Order: You arrange physical objects: You shelve books, you file papers, you put away your silverware.

Second Order: You arrange separate, smaller objects that contain metadata about the first order objects: You create a card catalog. You make entries in a ledger. You index a book. You now have a second organizational scheme (e.g., the books are shelved by subject but the cards are arranged alphabetically), and it's physically easier to navigate

Third Order: You create electronic metadata so you can organize it in ways that simply weren't feasible before.

Pyramid of Information

What is at the top