Windows LiveID is a single sign-on service provided and maintained by Microsoft. By integrating LiveID into your website, you can allow site visitors to log in to your website using their LiveID login and password.
More information about integration of Windows Live ID with Kentico CMS can be found in Kentico CMS Developer's Guide -> Membership and User registration -> Windows Live ID.
Page url: http://devnet.kentico.com/docs/5_5r2/communitysiteguide/index.html?liveid_overview.htm