Single sign-on (SSO) is a session/user authentication process that permits a user to enter one name and password in order to access multiple applications. The process authenticates the user for all the applications they have been given rights to and eliminates further prompts when they switch applications during a particular session.
With Teamwork Projects, SSO is enabled via SAML (Security Assertion Markup Language: an XML standard that allows secure web domains to exchange user authentication and authorization data). Essentially, it removes the need for your users to log into multiple applications in a particular browser session. Once they log into one system, it exchanges authentication / authorization data with another service you have SSO set up with and automatically logs the user in.
Single sign-on (SSO) is available only on Enterprise subscriptions, and if you wish to speak with a member of the enterprise team you can contact them from here.