XM usually refers to XM Satellite Radio.
In computing, Extensible Markup Language (XML) is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable.
XM Satellite Radio (XM) was one of the three satellite radio (SDARS) and online radio services in the United States and Canada, operated by Sirius XM Holdings.
Extensible Messaging and Presence Protocol (XMPP) is a communications protocol for message-oriented middleware based on XML (Extensible Markup Language).
An XML schema is a description of a type of XML document, typically expressed in terms of constraints on the structure and content of documents of that type, above and beyond the basic syntactical constraints imposed by XML itself.
XMLHttpRequest (XHR) is an API in the form of an object whose methods transfer data between a web browser and a web server.
XMM-Newton, also known as the High Throughput X-ray Spectroscopy Mission and the X-ray Multi-Mirror Mission, is an X-ray space observatory launched by the European Space Agency in December 1999 on an Ariane 5 rocket.
XSD (XML Schema Definition), a recommendation of the World Wide Web Consortium (W3C), specifies how to formally describe the elements in an Extensible Markup Language (XML) document.
The XM25 Counter Defilade Target Engagement (CDTE) System, also known as the Punisher and Individual Semiautomatic Air Burst System is an airburst grenade launcher derived from the XM29 OICW.
The XM8 was the military designation for a lightweight assault rifle system from the late 1990s to early 2000s.