SAML, or Security Assertion Markup Language, is an open standard used for exchanging authentication and authorization data between parties, particularly between an identity provider and a service provider. It allows users to log in once and gain access to multiple applications without needing to enter their credentials repeatedly, enhancing user convenience and security. SAML works by using XML-based messages to communicate user identity and access rights. When a user attempts to access a service, the service provider requests authentication from the identity provider, which then verifies the user's identity and sends a response back, allowing access to the requested resource.