XCross / eXchange / eXpanded / eXtended / eXtension / Transfer
X-)Cross Eyed
X2BheXadecimal to Binary
X2CheXadecimal to Character
X2DheXadecimal to Decimal
XAeXtended Architecturee / eXtended Attribute
XALSeXtended Application Layer Structure
XAPIAX.400 Application Program Interface Association
XBX-Bar (Crossbar)
XBARX-Bar (CrossBAR)
XBMX Bit Map
XBTCrossBar Tandem / X - Bar Tandem
XCMDeXternal CoMmanD
XCOSTTransfer Cost
XDFeXtended Density Format
XDReXtended Data Representation / eXternal Data Representation
XDSX/Open Directory Service
XFCNeXternal Function
XFEX-Bar Front End
XFMCCross Functional Management Committee
XFNX/Open Federated Naming (specification)
XGAeXtended Graphics Adapter/Array
XIDeXchange IDentifier
XIFXerox Image File
XIOSeXtended Input/Output System
XIPeXecution In Place
XMHX Mail Handler
XMLeXtensible Markup Language
XMMeXtended Memory Manager
XMPX/Open Management Protocol
XMSeXpanded Memory Service / eXtended Memory Specification / Extended Multiprocessor (operating) System
XNAXerox Network Architecture
XNSXerox Network Services/System
XOeXactly Once
XOFFTransmitter Off
XOMX/Open OSI abstract data Manipulation
XONTransmitter On
XOReXclusive OR
XPExperience (Common MUD term)
XPDCross Polarization Discrimination
XPGX.400 Promotion Group / X/Open Portability Guide
XPRMXerox Print Resources Manager
XPSDUeXpedited Presentation Service Data Unit
XQLXtructured Query Language
XRTeXtensions for Real-Time
XSMDeXtended Storage Module Drive
XSSDUeXpedited Session Service Data Unit
XSSIeXtended Server Side Includes
XSVTransfer Cost System Value
XTCExtended Test Controller / eXternal Transmit Clock
XTCLKeXternal Transmit CLocK
XTIX/Open Transport-layer Interface
XTLAExtended Three Letter Acronym
XTPeXpress Transfer Protocol / eXpress Transport Protocol
xxooxxooLove (or hugs) & kisses

XML Abbreviations            :-   Extensible Mark-up Language