X-Ray
High-frequency electromagnetic ray of short wave-length, capable of penetrating most solid substances.
X.25
International standard of the CCITT for packet switching.
X.400
CCITT recommendation designed to facilitate international message and information exchange between subscribers of computer-based store-and-forward services and office information systems in association with public and private data networks.
X.500
CCITT now ITU recommendations (ISO 9594) for the structure of directories for the maintenance of addresses used in electronic mail.
