Stakes.....money or property risked on a wager or gambling game.....AM Heritage Dict
Gamble....to bet on uncertain outcomes. to take a risk in hope of gaining an advantage or benefit...ibid
As long as your broker insists you put real money up when you buy or sell stocks and you expect to profit if the price goes in the direction you wish, and know you will lose money if it goes against you .....you are gambling. Regardless of the skill factor,, if there is any degree of uncertainy,,you are gambling.
Hi stakes Backgammon is a well known gambling game. Trading stocks belong to a type of gambling called proposition betting. In buying shares (being long) you are saying I will bet you the price of these shares will increase in value.
It is similar to a race track bet where you bet the five horse will win the race. Your odds may be better in the stock market but in both situations there is uncertainy and if you are wrong you will lose money.