A protocol consisting of XML-based request and response message formats for exchanging security information, expressed in the form of assertions about subjects, between on-line business partners.
Sources:
CNSSI 4009-2015
A framework for exchanging authentication and authorization information. Security typically involves checking the credentials presented by a party for authentication and authorization. SAML standardizes the representation of these credentials in an XML format called assertions, enhancing the interoperability between disparate applications.
Sources:
NIST SP 800-95
under Security Assertions Markup Language (SAML)
from
Glossary for the OASIS Security Assertion Markup Language (SAML) V2.0