SAML is a standard for exchanging security-related messages between different entities, most commonly used for single sign-on (SSO). In SSO, users authenticate with a centralized identity provider (IDP) and then access multiple applications without having to log in to each one individually. The service provider (SP) and IDP communicate via the user's browser, exchanging SAML requests and responses. SAML responses contain assertions about the user's identity, which are digitally signed by the IDP to ensure authenticity and integrity.