XGP
1. n. Xerox Graphics Printer.
2. v. To print something on the XGP. "You shouldn't XGP such a large file."

XYZZY
[from the Adventure game] adj. See PLUGH

YOYO
n. DEC service engineers' slang for UUO (q.v.). Usage: rare at Stanford and MIT, has been found at random DEC installations

YOYO MODE
n. State in which the system is said to be when it rapidly alternates several times between being up and being down

YU-SHIANG WHOLE FISH
n. The character gamma (extended SAIL ASCII 11), which with a loop in its tail looks like a fish. Usage: used primarily by people on the MIT LISP Machine. Tends to elicit incredulity from people who hear about it second-hand

ZERO
v. 1. To set to zero. Usually said of small pieces of data, such as bits or words.
2. To erase; to discard all data from. Said of disks and directories, where "zeroing" need not involve actually writing zeroes throughout the area being zeroed