We all bookmark.
If we are a blogger we tag.
Social bookmarking is when we share what we bookmark and tag.
By looking at bookmarks saved by others, users can discover new sources of information that might be missed by search engines.
We do this by saving our bookmarks on the web as well as on our own machine.
Then they can be accessed from anywhere.
Here’s a great article on social bookmarking.
Social bookmarking: Pushing collaboration to the edge