| Nom | Description |
| X.25 | CCITT recommendation for packet switched network DTE interfacing |
| X.400 | Electronic mail addressing and routing Protocol |
| X.500 | CCITT recommendation for distributed network directory services |
| X11 |
| X Windows release 11 |
| X window System version 11 |
| X12 | ANSI Electronic Data Interchange |
| X2B | Hexadecimal to Binary |
| X2C | Hexadecimal to Character |
| X2D | Hexadecimal to Decimal |
| X86 | Intel 80x86 microprocessor family |
| X |
| Cross |
| Exchange |
| Expanded |
| Extended |
| Extension |
| Transfer |
| XA |
| Extended Attribute |
| eXtended Architecture |
| XACT | Xante's Accurate Calibration Technology "Xante", "X*ACT" |
| XALS | eXtended Application Layer Structure |
| XAO | Technologie Assistée par Ordinateur |
| XAPIA |
| X.400 API Association |
| X.400 Application Program Interface Association |
| XB | X - Bar |
| XBAR | CrossBAR |
| XBASE | "language de programmation dBase Foxbase" |
| XBIU | eXternal Bus Interface Unit |
| XBM |
| X Bit Map |
| X Windows Bitmaps "file name extension" "black and white" |
| XBP | XBase Parts |
| XBT | CrossBar Tandem / X - Bar Tandem |
| XCA | External Communications Adapter |
| XCCI | X Common Client Interface, "X CCI" |
| XCEM | eXtensions for Control, Engineering and Manufacturing |
| XCHG | Exchange |
| XCHS | eXtended Cylinder Head Sectors |
| XCMD | External Command |
| XCMOS | eXtended CMOS |
| XCMS | X Color Management System, "Xcms" |
| XCOFF | eXtended Common Object File Format |
| XCOPY | Extended Copy |
| XCOST | Transfer Cost |
| XCUTS | X Commands and Utilities Test Suite |
| XCVR | Transceiver |
| XDF |
| Extended Density Format |
| Extended Distance Feature |
| XDM | X Display Manager |
| XDMCP | X Display Manager Control Protocol |
| XDR |
| Extended/External Data Representation |
| eXternal Data Representation |
| XDS | X/Open Directory Service |
| XENIX | "Unix Microsoft" |
| XES | Xerox Engineering Systems |
| XFCB | Extended File Control Block |
| XFCN | External Function |
| XFD | X Font Display |
| XFDL | Extensible forms Description Language |
| XFE |
| X - Front End |
| X Front End |
| XFMC | Cross Functional Management Committee |
| XFN |
| X/Open Federated Naming (specification) |
| X11 Federated Naming |
| XFS | eXtended File System |
| XGA |
| eXtended Graphics Adapter |
| eXtended Graphics Adaptor ( 1024 by 768 pixels ) |
| eXtended Graphics Array |
| XGL | X Graphics Language |
| XHTML | Extensible HyperText Markup Language |
| XID |
| Exchange Identification |
| Exchange Identifier |
| [SNA] eXchange IDentifier |
| XIDB | eXtended Integrated Data Base |
| XIE | X Image Extension |
| XIF | Xerox Image File |
| XIL | X11 Imaging Language |
| XIO | eXtended Input/Output |
| XIOS | Extended Input/Output System |
| XIP |
| eXecute In Place |
| eXecution In Place |
| XLA | Add In "file name extension" "Microsoft Excel" |
| XLAT | Translate |
| XLF | Exceptional Fortran |
| XLK | Backup "file name extension" "Microsoft Excel" |
| XLL |
| Extensible Link Language |
| Extensible Links Language |
| XLM | Excel Macro Language |
| XLR | Extra Long Run |
| XLS | Excel Spreadsheet |
| XLT | Template "file name extension" "Microsoft Excel" |
| XMAPI | eXtended Messaging Application Program Interface |
| XMH | X Mail Handler |
| XMI | eXtended Memory Interconnect |
| XMIT | Transmit |
| XML | Extensible Markup Language |
| XMM | eXtended Memory Manager |
| XMODEM | File transfer protocol |
| XMOS | High speed Metal Oxide Semiconductor |
| XMP | X/Open Management Protocol |
| XMS |
| Extended Memory Specification |
| eXtended Multiprocessor operating System |
| XMUX | Transmultiplexer |
| XN | eXecution Node |
| XNA | Xerox Network Architecture |
| XNB | Xodiac Network Bus |
| XNF | Xilinx Netlist Format |
| XNS |
| Xerox Network Services / Systems / Standard |
| Xerox Network System |
| Xerox Network System / Xerox Network Services |
| Xerox Network Systems |
| XNSCP | [PPP] XNS IDP Control Protocol |
| XNSIDP | Xerox Network Services Internet Datagram Protocol "Xerox, Internet","XNS IDP" |
| XNSITP | Xerox Network Services/Internet ??? Protocol "Xerox", "XNS/ITP" |
| XO |
| Crystal Oscillator |
| eXactly Once |
| XOFF |
| Transmitter Off |
| eXchange OFF |
| XOM | X/Open OSI abstract data Manipulation |
| XON |
| Transmitter On |
| eXchange ON |
| XOR | eXclusive OR |
| XOT | X.25 Over TCP |
| XP | Extreme Performance |
| XPC | X Performance Characterization [group] |
| XPD | Cross Polarization Discrimination |
| XPDS | Xerox Professional Document Services |
| XPG2 | X/Open Portability Guide release 2 |
| XPG |
| X.400 Promotion Group |
| X/Open Portability Guide |
| XPGR3 | X/open Portability Guide Release 3 |
| XPLA | eXtended Programmable Logic Array ( Philips ) |
| XPM | X Windows Pixelmaps "file name extension" "color" |
| XPRM | Xerox Print Resources Manager |
| XPS |
| eXPert System |
| eXtended Parallel Server |
| XPSB | X Protocol Stream Benchmark |
| XPSDU | eXpedited Presentation Service Data Unit |
| XQL | Xtructured Query Language |
| XRAM | eXtended RAM ( µC ) |
| XREF | Cross Reference |
| XRIP | eXtended ??? Routing Information Protocol |
| XRNS | Extensible Resource Name System |
| XRT |
| Extensions for Real Time |
| eXtensions for Real Time market data |
| XSL |
| Extensible Style Language |
| Extensible Style Language component |
| Extensible Stylesheet Language |
| XSLT | Extensible Stylesheet Transformation |
| XSMD |
| Extended Storage Module Drive |
| eXtended Storage Module Driver interface |
| XSSDU | eXpedited Session Service Data Unit |
| XSSI | Extended Server Side Includes |
| XST | eXperimental Stealth Tactical (Have Blue) |
| XSV | Transfer cost System Value |
| XSVF | Xilinx Serial Vector Format |
| XT |
| X window Toolkit |
| eXtended Technology |
| XTC |
| eXtended Test Controller |
| eXternal Transmit Clock |
| XTCLK | External Transmit Clock |
| XTEND | Xerox Telecommunication Network |
| XTI |
| X/Open Transport Interface |
| X/Open Transport-layer Interface |
| XTLA | Extended Three Letter Acronym |
| XTP |
| Xpress Transport Protocol |
| eXpress Transfer Protocol / eXpress Transport Protocol |
| eXpress Transport Protocol |
| XUI | X windows User Interface |
| XUIDL | X Unique ID Listing. "UIDL, POP3", "X UIDL" |
| XUL | Extensible User Interface Language |
| XUMA | eXpertensystem UMweltgefaehrlichkeit von Altlasten |
| XV | XView |
| XVIEW | X window system based Visual/Integrated Environment for Workstations |
| XVT | eXecutive Vector Table |
| XWD | X Window Dump |
| Xtal | crystal |
