SAML (Security Assertion Markup Language) is the XML-based standard behind most enterprise single sign-on. When you click a workplace app and land in it already authenticated, a SAML assertion from your identity provider, such as Microsoft Entra ID or Okta, did the work.
For IT evaluating workplace software, SAML support (or its modern sibling OpenID Connect) is a gatekeeper requirement: it means corporate authentication policy, including MFA and conditional access, applies to the workplace app automatically.