Update Services are tools you can use to let other people know you’ve updated your blog. WordPress automatically notifies popular Update Services that you’ve updated your blog by sending a XML-RPC ping each time you create or update a post. In turn, Update Services process the ping and updates their proprietary indices with your update.
You can also speed up this process, WordPress offer the chance for you to add update services in General > Writing. Scroll down to Update Services and add these.
You can find more XML-RPC Ping Services here.