Social bookmarking is the practice of saving bookmarks to a website and tagging them with keywords so others have access to them too. With a simple click I can share websites I find with anyone in the network.
This YouTube video does a nice job introducing a social bookmarking tool called Delicious.
Diigo seems to push social bookmarking one step further. Not only does it allow me to annotate or comment on websites I visit, but I can choose to let others view my comments, allowing for discourse between colleagues. In addition, Diigo allows users to create and join groups to further extend the bookmarking network. I enjoy this feature of Diigo immensely.
Look for lisettecasey on both of these sites.