Losing money is not fun at all, no doubt about it but that's not what is meant by "gambling for fun". People gambling for fun does not mean that they are looking for fun only, they want to make money for sure but they are also enjoying the game and losing some money will not affect their life.
This is true for gamblers who only used extra money for gambling.
Because you can have fun during the game if you are not worried about the money involved.
Even if you lose, that's fine. As long as you got the thrills and excitement while playing.
But if you are using a loaned money, without a doubt, you are not in anyway gambling for fun but to make money.
But of course, while playing with your extra money, there's a hope that you want to earn more.
If not, that's fine. That's gambling. But you enjoy the game without worries of returning the money back.