Some people feel that there really is no difference.
These are usually people who have done poorly in the stock market. The late Benjamin Graham defined an investment as a security purchase which promised safety of principal and a reasonable return. A bet in a casino violates the first requirement because you can lose all of the principal wagered. It also violates the second requirement because a casino bet can return many times the sum gambled, which in the business world is an unreasonable return. Remember the average U.S. corporation earns about 12 percent on the owners' money in a typical year.