The way I like to think of it is, it's gambling when your expected rate of return is negative or zero. It's investing when it is positive.
This is why a gambler is gambling, but a casino is investing/running a business.
Betting all your money on one hand of blackjack is a gamble, even if you've been counting cards and know the odds are in your favor. A casino spreading its money over millions of small bets is investing.
The best example would be bonds. If you buy the California Bonds... the people of California may get a High-Speed Railroad within a year. They will not be able to accomplish the building of the High Speed Railroad without investor support.
30 years from now, the state of California will finish paying off your bonds. And you'll make some money.
Win/Win for everyone. Investors make money, and California citizens get High Speed Railroads today... instead of 30 years from now.
There are people who make a living from this, just like there are people making a living from investments. Likewise, there are lots of people that lose at both.