The latter though is what a strategy is and not more of a calculated risk. But I do agree with your first definition that we should "gamble the money that we can afford to lose". And so even if we lose then nothing will be affected. We can wake up in the morning and not being traumatized by the money that we have lost the night before. And then maybe stop for a while, who knows.
With that, a gambler that uses calculated risk is more of a thinking gambler, a intelligent one. He knows what is at stakes and could make his bold decision to bet big or not stay away. This is in contrary of what we call YOLO gamblers.
For example, I have long developed a certain amount of money that is ready to lose for myself, but is not ready to spend more. Because I distributed a bankroll in stages and every stage I can spend a little more or a little less. I tried different options throughout my way in gambling and this seemed to me the most suitable. I will not have an option when I lose at a time too much and then I have been sitting without a game for a month. It becomes not comfortable for me and I want to play more, but if I do it, it will affect my life needs and my family, and in no case can I allow it