Y2K:

1. Year 2000, a reference to a anticipated doomsday when computer applications incapable of distinguishing centuries in dates would trigger the collapse of all civilization and the end of all life on earth.
2. Petty optimism by pessimistic engineers.
3. A money-making scam whereby enterprising developers convinced frightened managers to invest millions to fix problems that never existed. Cannot be duplicated until Y10K, so enough time may pass so no one will remember the hype.

YAML:

1. Yet another markup language.
2. The usual sound made by project managers as they bloviate.
3. Conclusive proof that, when developers want to simplify programming, they fail.

Yahoo!:

1. 1. Web! Based! Search! Engine!
2. 2. Internet site which, having failed to become a popular search engine, has developed countless ways for consumers to avoid making them profitable. 
3. 3. An exclamation, antithetical to those often uttered when the unsuspecting blunder upon their web site.

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