SAML is an open standard for transmitting authentication and authorization data between applications. That means that you can use the SAML protocol to use Teamstack to log in your users into a number of service providers. This process is called "Single Sign On" or SSO for short.
You can manage all your users in Teamstack and give them access to the apps they need. With a single login to Teamstack, your users can access multiple apps without the need to log in to every application separately.
For SAML to work, the service provider needs to support SAML 2.0. Most service providers also require you to have a specific plan that supports SSO via SAML. Check the services documentation for more info.