SAML
In plain terms
An XML standard for exchanging authentication between systems.
Going deeper
SAML lets identity providers assert a user's identity to service providers for single sign-on, common in enterprises. It predates OIDC.
Under the hood
XML-based assertions enable enterprise SSO; heavier than OIDC, which is now often preferred for new apps.
Examples
Enterprise SSO, identity federation, Okta/ADFS, corporate logins.
Think of it like...
Like a trusted notary vouching for your identity to other offices so you don't re-prove it.