Single Sign On (SSO) is the process of authenticating once against a single system to gain access to multiple (often unrelated) systems.

Single Sign On (SSO) is the process of authenticating once against a single system to gain access to multiple (often unrelated) systems.

SSO is not to be confused with shared authentication systems like Facebook Connect or Open ID - which require you to enter the password for one account once on each site you use it in order to gain access.