/məl-teks/
n. [from "MULTiplexed Information and Computing Service"]
An early (late 1960s) timesharing operating system co-designed by a consortium including MIT, GE, and Bell Laboratories. Very innovative for its time -- among other things, it introduced the idea of treating all devices uniformly as special files. All the members but GE eventually pulled out after determining that second-system effect had bloated Multics to the point of practical unusability (the 'lean' predecessor in question was CTSS). Honeywell commercialized Multics after buying out GE's computer group, but it was never very successful (among other things, on some versions one was commonly required to enter a password to log out). One of the developers left in the lurch by the project's breakup was Ken Thompson, a circumstance which led directly to the birth of UNIX. For this and other reasons, aspects of the Multics design remain a topic of occasional debate among hackers.
See also brain-damaged and GCOS.