What is the exact definition of happiness?

What is the exact definition of happiness?

As we see different people in different kind or we see one people in different way, both ways they seem they are happy. But the question is, they are really happy?

As for example, I knew a person who is always talking about his uncomfortable about his job, he always feels shame for his job and curses his financial condition as well. Yeah it’s true that as the post he is working is not get him well and make him a rich man. But he is working the same job day-to-day, year-to-year constantly. And when we gave them the idea why not you do something else sidewise (in the spare time when you are free from your day job) after your job. He said to us nothing and continued his job. 

I don’t like these peoples who only gave the ideas to others and always think that they are well known about everything. The people which I taken an example is the same. He think nobody clever than me.

Then in this situation I never understand where is the exact happiness is existing. To curse himself, his creativity or what? Is he really happy about his life? Is he really happy about his job? He is happy about his days?