The examples don't hold in most jurisdictions (except for the stock market and if short sells are allowed).

All of the three categories are defined as gambling in pretty much all jurisdictions across the globe. However, they are classified as different types, e.g. roulette is closer to slots than poker is. Then poker can be "cash tables" vs "tournament". The main classifier difference is "game of chance" vs "game of skill", yet there are lots of nuances.