There are many ways to use the financial markets that are not gambling. Buying an index fund or Coca-Cola isn’t gambling; it is not even very risky. Nor are individual stocks gambling, as you can get a reasonable idea of what a company’s price ought to be and how it is likely to perform in the future, at least for well-established companies. It’s also harder to get into debt, as long as you don’t short, because you can only spend money you have, and the stock does not become worthless if your analysis is wrong. (At least, there are warning signs)
Now day-trading? I consider that gambling, because any particular day’s price movement is a lot closer to random.
Buying a stock or mutual fund is the very definition of gambling: placing a monetary bet on an unknown future event. Just because this activity has historically had a +EV, doesn't make it any less gambling.
Purchasing a business or parts thereof is not “gambling” any more than purchasing a house is “gambling”. People purchase them (or are supposed to) for the value they provide either through income or asset appreciation in the case of businesses or shelter in the case of the house and not for the singular promise of some winning outcome unlike games of chance. The only expectation is that the asset purchased will continue to provide value throughout the period of ownership which is no more or less than what you would expect of many other assets or goods you might purchase and none of this is contingent on mere chance alone. Just because somebody quotes a ridiculously high or low price does not necessarily mean the intrinsic value of the asset has changed. Overpaying for an asset is not the same as losing money to a slot machine. Have I “lost money gambling” if I buy something in a store the day before it gets discounted? These are just risks that exist in any market. Do not confuse this issue just because some have decided to use them as mere vehicles for price speculation. People speculate on the price of eggs, oil and gold as well but that does not mean buying eggs for breakfast, fuel for your car or a gold necklace for your wife is “gambling”.
By this definition prime loans are also gambling. When you bet on something risky then you are gambling. When you bet on something not risky you are not gambling. Also consider that not investing will generally lose money over time due to things like inflation. If we define the goal to be holding as much value as we can, holding dollars is more risky than investing in many stocks (or bonds, which also have a risk of defaulting). A better definition of gambling is something like "taking unnecessary and unproductive risks."
I'm not sure I buy any definition of gambling that depends on the outcome. If you lose money or tend to lose money, then it's gambling, but if you win money or tend to win money, then we change the name to "investing?" Risk includes upside and downside risk.
It doesn't depend on the outcome. If a bank only does prime loans and spreads out it's loans multiple borrowers, has a good reserve ratio etc. and still loses it all, that still wasn't gambling. This is more clear if you consider that storing value in money is also risky. When you get paid in a currency, you automatically begin investing in it at the same time. This is even more clear with foreign currencies. If you got paid $1 million in Turkish Lyra and do not store that value somewhere else, that is more gambling-like than putting it in the S&P. I guess you can say that any time you increase the amount of risk in an investment to get more reward you are gambling. But you can invest in something other than USD with the same risk but with greater reward. For example you can invest it in US bonds (over multiple issues) which has a similar risk to the USD but a greater reward. Still, under such a definition, any business is gambling. We can accept that, but then we have no word that differentiates owning a grocery store from betting all your money on a coin flip, so then the word "gambling" becomes much less useful or really useless in my opinion.
Is it gambling if it has a +EV?