from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The time during which a device, such as a computer, is functioning or available for use.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The period of time a computer has functioned since last requiring a reboot.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a period of time when something (as a machine or factory) is functioning and available for use
up (adjective, computing) + time (Wiktionary)