Without looking up the textbook definition of gambling I have to say that "it depends". It's certainly not the type of gambling that millions of slot machine and VLT players lose billions of dollars at every day. That type of gambling you CANNOT make a living at year after year. You can strike it rich on occasion, but you cannot do anything to ensure that you CONTINUE making money.
However, some professional card players make a living year after year for their entire careers at this game. What exactly are they gambling if they KNOW that their skill at the game AND at
bankroll management will guarantee that they never lose more money than their poker BUSINESS can afford (over the course of a year for instance).
How can they be GUARANTEED not to lose money in the long term? By knowing when to stop, regroup, study, meditate, network, and discuss what they are doing wrong, and figuring out what to do to fix it.
Do most of us fall into this latter category? Absolutely not. For most of
US poker IS gambling. Why? Because most of us don't have the discipline and dedication to make the right decisions when facing down a losing streak.
But, most of us can also learn from the pros, and work to become disciplined enough to limit our losses and take the time to learn from our mistakes. And, if it just isn't working out - know when to quit for good. I don't have the skill to be a professional poker player. BUT, I've been playing real money poker for years and have not lost money at it. I am definitely not a gambler.