Answer Description
Single Sign On (SSO) describes the process of allowing a single set of credentials to validate a user across multiple independent systems. This is very common among Windows and Microsoft products, for example using Active Directory credentials on a SharePoint site collection.
Wikipedia
Single sign-on (SSO) is an authentication scheme that allows a user to log in with a single ID and password to any of several related, yet independent, software systems True single sign on allows the user to login once and access services without re-entering authentication factors It should not be confused with same-sign on (Directory Server Authentication), often accomplished by using the Lightweight Directory Access Protocol (LDAP) and stored LDAP databases on (directory) serversA simple version of single sign-on can be achieved over IP networks using cookies but only if the sites share a common DNS parent domainFor clarity, a distinction should be made between Directory Server Authentication (same-sign on) and single sign-on: Directory Server Authentication refers to systems requiring authentication for each application but using the same credentials from a directory server, whereas single sign-on refers to systems where a single authentication provides access to multiple applications by passing the authentication token seamlessly to configured applications
Single_sign-on - Wikipedia, the free encyclopedia