SSO, or Single Sign-On, is a single authentication method that allows users to enter their password only once to connect to multiple applications. SSO also allows retrieving information (first name, last name, etc.) to avoid having to enter it again when creating an account on an application.
Not all applications are "SSO-able," which often makes the SSO system partial. Furthermore, SSO does not always allow managing access rights on accounts, and application administrators must do it manually.