What is an Antihero?

The term antihero (or anti-hero) gets thrown around fairly often nowadays, sometimes incorrectly. The concept of an anti-hero is not technically new, but it certainly is prevalent in modern story-telling. The term itself was coined in the 18th Century, but examples of such a type of character are there in Greek drama, Roman satire and Renaissance literature. So what is an anti-hero, exactly? Simply put, an anti-hero is a main character of a story that does not have the typical qualities that are expected of a hero. This does not mean all antiheroes are bad people, just that they do not fit the traditional description of a hero.