Both involve handicapping. In horse racing, you're handicapping all the variables you know. In trading, you're handicapping (or at least you should be) behavior of the players as a group. By my definition, trading is definitely NOT "gambling". Seems to me handicapping the ponies might also not be gambling for one with enough information and gray matter.
It's easier to name the differences, where the first and most important one is that in a horse race, you lose your bet if you lose, which is usually not the case when investing.
They're both a kind of parimutuel betting. You're not betting against the house, you're betting that the other bettors are wrong, and you're betting against them. Of course, the stock market is not zero sum.
no kidding, if they would let me sit at a craps table in Las Vegas and bet on what the players will probably do I could pay for my rent.
With both, you are not 100% sure of the outcome. No matter the research, there is no 100% guarantee. Even if fixed, there is still not a 100% chance. so, that is gambling. the question is the payout versus money involved. I'm guessing horse betting can turn $1 into a lot. so more gambling. in trading, stock with cash, that is more rare. so less of a gamble. bet on earnings? there is a reason we say "bet". because we know the payoff is big if right.... everything in life is a gamble.....so just use common sense. oh, you want to turn 10k into 1 billion and call it 100% risk free? no
I had a friend who got a job training horses out there at Bay Meadows early in the morning. He was just a little itty biity guy, about half the size of a normal human being. I asked him if the races were fixed He said, "The one you have to watch out for is the one that is not fixed. In that race, anything can happen."
They are similar in the sense that if you need absolute certainty in your life - that trading and gambling are not your line of work. The other comments about probabilities are relevant.
Horse racing are like buying puts and calls (no nakedness) options: You know ahead of time how much the risk and reward is.
Horseracing is all about finding mispriced horses, odds that are out of wack based on your analysis. That way your payoff over time is large enough to cover the house take and losses. and yes, its paramutual meaning you're betting against other bettors, not the house.