Social Bookmarking is a way of sharing resources you find on the web with others.
A good description of social bookmarking can be found at Social Bookmarking in Plain English by CommonCraft.
Sample Sites:
Allows user to tag sites, search by tag, subscribe to another user's bookmarks, and search other user's bookmarks
Allows user to tag sites, add sticky notes to web pages, highlight information, share bookmarks within a group
Guides user through use of tagged sites, annotate sites, share trails, RSS to trails
My Web2.0 in Education Trail: http://www.trailfire.com/misstizzypc/trailview/57779
Example: http://www.trailfire.com/smeech/trailview/37762?q=technology%20in%20education