Having a hard time figuring out where or whether we diverged here. Sounds like we agree that prices have to fluctuate. Do we agree that if prices generally fluctuate up it's inflation and if they fluctuate down it's deflation?
Yes. The keyword is generally.
If beef prices go up because of a drought in beef-producing regions, that's not inflation. That's just supply and demand. But if it's the 15th Century, and the mediums of exchange are gold and silver, and the Conquistadors bring back boatloads of new gold and silver from the New World, and prices rise generally, that's inflation.
The prevailing theory is that the price level (P) is a function of the money supply (M), the rate at which it circulates (V), and the total amount of goods and services in the economy (y):
MV = Py
So, if the money supply, in combination with the rate of circulation rises faster than overall economic output, you get inflation. The explanation as to why the Fed's "quantitative easing" has not caused more inflation is that the money hasn't circulated much, being not loaned out by the banks, but rather, kept on deposit at the Fed by the banks.