What is Cross App SSO?

I am upgrading to essentials from free but see it doesn’t support Cross App SSO. What exactly is that? The tooltip says:
“Give your customers, partners and employees the freedom of Single Sign On while keeping the control and enhanced security you need”

I have no idea what that means. Can anyone explain?

I have the same question, My case I have 3 apps in auth0 and I want to be able to signing with my Auth0 username in the 3 apps