Social bookmarking allows users to store, organize, and share bookmarks of webpages online. It began in 1996 and grew rapidly, with early social bookmarking sites including Backflip, Blink, and del.icio.us launching in 2003. Social bookmarking introduces human classification of websites through user-assigned tags, which helps users find relevant pages and provides a ranking system. However, inconsistencies in tagging, such as spelling errors or ambiguous tags, can impact search results. Popular sites where tagging is used include del.icio.us, Flickr, and Gmail.