A farce is a broad satire or comedy, though now it's used to describe something that is supposed to be serious but has turned ridiculous. If a defendant is not treated fairly, his lawyer might say that the trial is a farce.
As a type of comedy, a farce uses improbable situations, physical humor and silliness to entertain. Spoof films such as "Spaceballs," a comedy based on the Star Wars movies, are farces. If a real-life event or situation is a farce, it feels this ridiculous. An election is a farce, if the outcome has been determined before the voting begins. And class can feel like a farce if your substitute teacher knows less about the subject than you do.