Its all been said, but just sat down with my coffee, so I will add here as well.
Poker is definitly gambling when it is played by some people. And it is these people that allow people like me to believe I have a chance to maybe make a small (define "small" lol) income with it, and it is these people that certainly contribute big to pro players ROI.
If the hand goes to showdown, then the gambling part can come into play. But that will depend on a number of things. Lets say you put your opponent on a High A due to his past play when he limped in MP and called your 4x raise from the button with TT. The flop comes K T 4 RB. he checks and you, trappy and sneaky player that you are, check behind. You are now convinced that he has the Ax. Turn is A. he bets 1/2 pot and you call. river is 5, no flush draw. he bets 3/4 pot, you go all in, he calls.
OK, now we come to SD. If he has that AX, were you gambling? Because you were using your information on him to make your decision to invest your money, I say no. If he has KK or JQ and was just being more trappy than you, does that change the answer to "yes"? I dont think so. What has happened in that case is that you have invested money to increase your information pool, and now know this players tendencies better, and can adjust your play against him in future battles. If you went to showdown purely on the strength of your trips, and did not lose too much thought over your opponents holdings, then this hand was a total gamble for you.
Next hand. You are on the button with Q9s. A SnG, 5 left, blinds 100-200. It is folded to you, and one fold is an extremely SS. You have an slightly larger stack than the blinds, you all have between 10-14 BB. So you go all in against the blinds. You believe the blinds are both decent players, so is this a gamble, or a good decision seeing as a player is about to blind out, and no one is going to risk their tourney life unless they have a premium hand? Win or lose, these decisions are based on thought and information, so, while a risk is certainly present, there are more factors influencing the outcome than just the cards.
This is the deciding factor here. Why you do what you do. And that is why the real answer to the question "Is poker gambling?" would be: