What is Single Sign$-$on $($SSO$)?$

A mechanism of digitally "signing" Ify information exchanged between applications$/$systems$.$

A mechanism which enables using single physical "signature" to do all banking transactions!

None of the above options.

A mechanism that enables a user to sign$-$in$/$login$/$authenticate to an application$/$system with their credentials only once, and then seamlessly access other applications$/$systems avallable in the same domain of trust $($e$.$g$.$ intranet portal of an organization$).$