Yes, "knockout" (knock-out) was synonymous with "time 0" when I first started brewing in the early nineties (as in knocking out the flame). At that point in time, the process of draining/pumping the wort out of one's kettle was referred to as "casting out." If you read John Palmer's book (which was written in the nineties), you will see that he uses the term as a synonym for "time 0."http://www.howtobrew.com/section1/chapter5-1.html
When hops are added during the final minutes of the boil, less of the aromatic oils are lost to evaporation and more hop aroma is retained. One or more varieties of hop may be used, in amounts varying from 1/4 - 4 oz, depending on the character desired. A total of 1-2 oz. is typical. Finishing hop additions are typically 15 minutes or less before the end of the boil, or are added "at knockout" (when the heat is turned off)
and allowed to steep ten minutes before the wort is cooled. In some setups, a "hopback" is used - the hot wort is run through a small chamber full of fresh hops before the wort enters a heat exchanger or chiller."
While the term "knockout" was borrowed from the professional brewing lexicon, the term "flameout" appears to be a 100% amateur brewing term. I have yet to see it printed in any professional brewing textbook.