Any investment can be seen as a “bet”, the difference comes from the conditions out of which the return comes. Does it come out of a business’s operations, or a piece of some other source of income? Then even a high-risk investment is still an investment. Even an investment in an asset which is expected to appreciate in the future is still an investment, as long as that appreciation is based on something tangible. Walt Disney bought up a lot of useless real estate in the Florida Swamp, but had a plan as to how to make the investment pay off.
A gamble will have nothing concrete backing it, it will just be down to chance. Like betting on Red at Roulette. Or going to FanDuel and betting that Pete Alonso will hit a home run in tonight’s game. Those odds are made by professional bookmakers to make the chances as close to 50/50 (minus the sports book’s vig) as they can.
Basically, a gamble is up to random chance, an investment can be backed by a business case. But there are aspects of risk to both.