YP: Yellow Pages protocol
The Yellow Pages (YP) protocol, now known as Network Information Service (NIS), is a directory service used for name look-up and general table enumeration. Each YP database consists of key-value pairs, maps, and domains. YP defines a set of key-value pairs as a map. Each map belongs to a domain that is a category of maps. This hierarchy of key-value pairs, maps, and domains provides a generic structure for modeling a database of information. An optional component to a YP server database implementation is the YP binder (YPbind) server. YP uses YP-binder servers to provide addressing information about YP database servers to potential clients.
Standard Organization: Sun

Ymodem
YMODEM is a protocol for file transfer used between modems. YMODEM was developed by Chuck Forsberg as the successor to XMODEM and MODEM7. The original YMODEM was essentially the same as XMODEM except that it sent the file's name, size, and timestamp in a regular XMODEM block before actually transferring the file. Sending the file size solved XMODEM's problem of superfluous padding at the end of the file.

ZigBee
ZigBee, defined in the IEEE 802.15.4, is the technology used in the low data rate Wireless Personal Area Network (WPAN) for home control, building automation industrial automation. ZigBee covers up to 330 feet (about 100 meters) in the bandwidth of 20 to 250 kbps.
Standard Organization: IEEE
Reference Document: IEEE 802.15.4

ZIP: Zone Information Protocol
Zone Information Protocol (ZIP), an AppleTalk session layer protocol, manages the relationship between network numbers and zone names. ZIP is used by NBP to determine which networks contain nodes that belong to a zone.
Standard Organization: Apple

Zmodern
ZMODEM is a file transfer protocol developed by Chuck Forsberg in 1986, to improve file transfers over X.25 network. In addition to dramatically improved performance compared to older protocols XMODEM and YMODEM, ZMODEM also offered restartable transfers, auto-start by the sender, an expanded 32-bit CRC, and control character quoting, allowing it to be used on networks that might "eat" control characters. ZMODEM became extremely popular on bulletin board systems in the early 1990s, displacing earlier protocols such as XMODEM, YMODEM and JMODEM.