What is a commercial film ?

I don't understand what a commercial film is.
When some one pays money to watch that specific film, then it becomes a commercial film because it involves commerce or business where the transaction of money takes place. If that's the case all films are commercial films.
Some people say no! ,only when a film becomes a hit it's a commercial film, i ask you a question, what's hot film, they say it runs well and earns profit, i again ask who earns profit. As far as i know only 2 percent of the whole Indan cinema becomes hit, as per the data given by producer council, so do we make only 2% commercial films, rest is all Non-commercial or art film or what do you call it. Then Tanga Manasukaran is a art film.
Some people say it should have all commercial elements like sex, violence and hot songs, then what do you call Salam bombay because i, as far as i have seen al most all so called art films have either sex or violence in a greater content than normal films.
What is a commercial film.