SSO, or Single Sign-On, is a unique authentication method that allows users to enter their password only once, in order to connect to several applications. SSO also makes it possible to retrieve information (first and last names, etc.) so that users don't have to re-enter it when creating an account on an application.
Not all applications are "SSO-ready", which means that SSO is often only partial. What's more, SSO doesn't always allow account access rights to be managed, and application administrators have to do this manually.