What is wrong with the popular definition of inflation?

According to Mises,

"Inflation, as this term was always used everywhere and especially in this country, means increasing the quantity of money and bank notes in circulation and the quantity of bank deposits subject to check. But people today use the term `inflation' to refer to the phenomenon that is an inevitable consequence of inflation, that is the tendency of all prices and wage rates to rise. The result of this deplorable confusion is that there is no term left to signify the cause of this rise in prices and wages. There is no longer any word available to signify the phenomenon that has been, up to now, called inflation."

In short, what today is called inflation is the general rise in prices, which is in fact only the outcome of inflation. Consequently, anything that contributes to price increase is called inflationary and therefore must be guarded against.

Thus a fall in unemployment or a rise in economic activity are all seen as potential inflationary triggers and therefore must be restrained by central bank policies. Some other triggers such as rises in commodity prices or workers wages are also regarded as potential threats and therefore must be always under the watchful eye of the central bank policy makers.(...)

We have seen that increases in the money supply set in motion an exchange of nothing for something. They divert real funding away from wealth generators toward the holders of the newly created money. This is what sets in motion the misallocation of resources, not price increases as such, which is only the manifestation of this misallocation.

Moreover, the beneficiaries of the newly created money, i.e., money out of "thin air"—are always the first recipients of money, and so they can divert a greater portion of wealth to themselves. Obviously, those who either don’t receive any of the newly created money or get it last will find that what is left for them is a diminished portion of the pool of real funding.

Additionally, real incomes fall not because of general rises in prices, but because of increases in the money supply, which gives rise to nonproductive consumption. In other words, inflation depletes the real pool of funding, which undermines the production of real wealth—i.e., a lowering of real incomes.

General increases in prices, which follow increases in money supply, are an indication that the erosion of peoples’ purchasing power has taken place. It is not the symptoms of a disease but rather the disease itself that causes the physical damage. Likewise, it is not a general rise in prices but increases in the money supply that inflict the physical damage on wealth generators.(...)" Is the Fed an Inflation Fighter or Creator? by Frank Shostak