A cross-platform, extensible, and text-based standard markup language for representing structured data. It provides a cross-platform, software- and hardware-independent tool for transmitting information.
Sources:
NIST SP 800-95
under Extensible Markup Language (XML)
from
World Wide Web Consortium (W3C): Extensible Markup Language (XML)
a flexible text format designed to describe data for electronic publishing.
Sources:
NISTIR 7250
under Extensible Markup Language
NISTIR 7387
under Extensible Markup Language