XACML (eXtensible Access Control Markup Language) is an OASIS standard for defining and interpreting access control policies across multiple security domains. It provides a policy language and request/response protocol for making authorization decisions based on attributes. XACML policies can be defined in terms of attributes for subjects, resources, actions, and the environment, allowing for fine-grained and context-aware access control (ABAC). The XACML architecture separates policy enforcement from decision making and includes policy administration, information, and retrieval points.