What's so honest about being Earnest?

How is The Importance of Being Earnest a "comedy of manners"? What does this mean? How has it been shown in the play already?

Well, I think that it has been funny because the characters are pretty much making fun of the way society is during that period of time. The two main characters both represent the "manners" that are expected from the rich people who have nothing else to do than stay home, eat, sleep and bother other people. They take mostly everything as a joke, specially marriage. They think life is a joke as a whole, and like they could get everything they want because they are rich, and do not know how to appreciate the things they have and that others don't. So, far, is like a play making fun of society. (forgot the formal word for this).