Single Sign-On (SSO) is an authentication process that allows a user to access multiple applications with one set of login credentials, across domains. Essentially, there is a central domain through which authentication is performed, and then the session is shared with other domains.
A real-world example of SSO authentication is Google’s suite of online applications. Log into a single Google application and then you are able to access other Google applications as well, thereby saving the task of reentering password every time you toggle between your Gmail Inbox and Google Drive.