I don't really know if similar question or concerns has been raised before, we often say that we are gamblers but does it mean that anyone who gambles once or twice is a gambler? If no, how long could someone be classified as a gambler?
You really need to understand that there are levels of addiction. Yes, we're not talking about that, but when one decides to try out something they once tried, which is kind of odd looking, but they still feel like they need to try it more often, that's the stage-one type of addiction. So to answer your question, yes.. if you gamble once or twice in a week, month, year - regardless of how small the period looks to you, it doesn't change the fact.
or what games that are to be classified as someone gambling.
What in the heavens is this?? Boy, you don't need no type of classifications on something you put your hard-earned money on. As long as your funds are into it, and you're patiently expecting something off of it, you're gambling. Doesn't really matter on what type of games -- you could decide to kick plastic/disposable containers with your homeboys and put that money on it if you're good at it.