XOFF – An ASCII character that tells the transmitting device to halt transmission.
XON – An ASCII character that tells the transmitting device to resume transmission.
XLR Plug – A three-pin audio connector that can be used with three-wire balanced cables, which cause electro-magnetic interference to be canceled out.
XML – Short for Extensible Markup Language, a specification developed by the W3C World Wide Web Consortium. XML is a pared-down version of SGML Standard Generalized Markup Language, designed especially for Web documents. It allows designers to create their own customized tags, enabling the definition, transmission, validation, and interpretation of data between applications and between organizations.