Assurance Level (IAL / AAL / FAL)
NIST SP 800-63's three independent dials — identity proofing, authenticator strength, and federation strength — each rated 1 to 3, for stating exactly how strong each part of a system must be.
aka: IAL, AAL, FAL, NIST assurance level
Instead of one fuzzy “security level,” NIST splits assurance into three independent questions: how sure are you the person is who they claim (IAL), how strong is the login itself (AAL), and how strongly does a federated assertion carry that proof across systems (FAL). A use case can mix levels — light identity proofing with strong authentication, or vice versa — because the risks they cover are genuinely different.