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 a property of access control of multiple related, yet independent, software systems With this property, a user logs in with a single ID and password to gain access to any of several related systems It is often accomplished by using the Lightweight Directory Access Protocol (LDAP) and stored LDAP databases on (directory) servers A 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 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