If there are Web sites that you visit often or that you would like to keep as a reference to come back to, it is easy to use your browser to “bookmark” them. This means that you store the URL (uniform resource locator) so that you can locate it again easily. It also gives you a personal library of Web sites that you can store on your computer.
Social bookmarking sites, however, allow you to store these links online, use tags to describe them, and share these lists with other users. Some of these sites let you submit URLs that other users vote on, while others allow you to use the saved tags to browse through the lists and libraries that have been generated
