Poker is gambling, however I think the "gambling" part is inversely proportional to the player's skill level. I could argue that the stock market is also gambling on some levels too, mainly because of the "put your money in and hope you get it back" part of it, which is also a function of what type of stocks you're buying. Buying stocks off the pink sheets on margin? Methinks that's pure gambling. Buying shares of an index fund? Not nearly as much.
But, vocabulary aside, any activity where you take a risk and cannot completely control or predict the outcome can be called gambling too. Driving nowadays with all the idiots behind the wheel who spend more time texting than looking at the road is also a significant gamble.