SAML (Security Assertion Markup Language) is an XML-based standard used to enable Single Sign-on (SSO) by allowing an identity provider to provide authentication across multiple services with a single login. It's supported by every major IdP in use today and allows users to sign in once and access multiple applications without signing in again. SAML assertions can include Authentication, User Attributes and Authorization Decisions. SAML is commonly used for Single Sign-on (SSO), Attribute Exchange, and User Provisioning. Alternatives to SAML include OpenID Connect and OAuth.