SSO (Single Sign-On) allows a user to authenticate once and gain access to multiple systems or applications without needing to log in again for each resource. RADIUS is a centralized authentication protocol but does not inherently provide single sign-on. MFA (Multi-Factor Authentication) adds additional authentication factors but does not consolidate logins. TACACS+ is an authentication protocol used primarily for network devices, not for enabling SSO across multiple applications. SSO is the correct choice for enabling access to multiple resources with one account login.