What is social bookmarking?
Social bookmarking is a technique for managing the URLs of your favorite websites with an online service and being able to share these bookmarks with others. In contrast to managing bookmarks with a browser’s built-in features, your bookmarks not necessarily need to be private to yourself, but others can browse through your bookmarks as well. Vice versa, you can browse through other people’s bookmarks and discover new, interesting sites.
How are these services distinct from a browser’s built-in feature?
Your bookmarks are not locked into one browser or even one device (if a browser doesn’t support cross-device synchronization): Depending on the social bookmarking service, you can access your bookmarks from any device, even on the go via mobile websites or mobile applications.
Is social bookmarking a new trend?
Definitely: no. Social bookmarking is nothing new: The first online services for managing bookmarks were launched back in 1996. According to Wikipedia, itList was one of the first services for managing and sharing URLs of interesting websites. However, the term “social bookmarking” became popular when Delicious (del.icio.us) launched its service in 2003. They were one of the first services that established “tagging”, a feature for adding keywords to items (here: bookmarks). Tagging was considered so useful that many other websites such as Flickr integrated it into their services.
How many social bookmarking services exist?
Well, that’s hard to say. At the time of writing, Wikipedia lists about 25 active services. I guess this list is by far not complete. This page lists more than 50 social bookmarking websites with German content. I think there are way more than 100 social bookmarking services in total.