- Worst-case scenario
- Worsted
- Wound
- Wound assessment
- Wound bed preparation
- Wound dehiscence
- Wound healing
- Woven
- Woven fabric
- Wrapped normal distribution
- Wrapper
- Wrapping
- Wrench
- Wrinkles
- Wrist
- Write
- Write buffer
- Writhe
- Wrought iron
- Ws-security
- Wuchereria bancrofti
- Wulff construction
- Wurtzite
- Wyckoff positions
- Wythe
- X chromosome
- X-gal
- X-inactivation
- X-linked
- X-linked recessive
- X-ray absorption fine structure
- X-ray absorption near edge structure
- X-ray absorption spectroscopy
- X-ray crystallography
- X-ray detectors
- X-ray emission spectroscopy
- X-ray filter
- X-ray lasers
- X-ray lithography
- X-ray microscopy
- X-ray microtomography
- X-ray notation
- X-ray optics
- X-ray photoelectron spectroscopy
- X-ray raman scattering
- X-ray reflectivity
- X-ray scattering
- X-ray scattering techniques
- X-ray standing wave
- X-ray tubes
- X-rays
- X-y tables
- X10
- X3D
- X86-64
- XACML
- XAMPP
- XANES
- XBRL
- XBee
- XForms
- XLD agar
- XML
- XML Schema
- XML database
- XML metadata interchange
- XML namespaces
- XML tree
- XML-RPC
- XMLHttpRequest
- XMPP
- XNOR gate
- XOR gate
- XPDL
- XPS
- XPath
- XQuery
- XRCC1
- XRF
- XSL
- XSLT
- XVIII
- Xanthan gum
- Xanthate
- Xanthine
- Xanthine dehydrogenase
- Xanthine oxidase
- Xanthine oxidase inhibitor
- Xanthomonas campestris
- Xanthomonas oryzae
- Xanthone
- Xanthophyll
- Xantphos
- Xcode
- Xen
- Xenobiotics
- Xenoliths
- Xenon
- Xenon arc lamps
- Xenon hexafluoroplatinate
- Xenon-135
- Xenotime
- Xenotransplantation
- Xeon
- Xeon Phi
- Xeroderma pigmentosum
- Xerography
- Xerophthalmia
- Xerostomia
- Xfoil
- Xgboost
- Xiaoice
- Xilinx ISE
- Xofigo
- Xonotlite
- Xplore
- Xylanase
- Xylene
- Xylenol
- Xylidine
- Xylitol
- Xyloglucan
- Xylooligosaccharide
- Xylose
- Xylose isomerase
- Xylose metabolism
- Xylulose
- Xylulose 5-phosphate
- Y box binding protein 1
- Y chromosome
- Y-intercept
- Y2K
- YAG
- YAGO
- YAML
- YBCO
- YIG
- YIG spheres
- Yagi antenna
- Yang
- Yard
- Yarn
- Yaw
- Yaw damper
- Yaw rate sensor
- Yaw-rate sensor
- Ybus matrix
- Year 2000 problem
- Yeast
- Yeast extract