From the introduction:
Welcome to the Dungeon Crawl Unlimited roleplaying game system. For those new to them roleplaying games (RPGs) involve one game master (GM) and two or more players. Each player takes on the persona (controls or runs) a character (player character or PC) in the game. The game itself takes place in a different world, a
different time or even a different reality. It may even be the modern world with a strange twist or three. The GM sets the stage and the players decide what their characters will do within it.
In many ways a roleplaying game is like a movie or TV series with the PCs as the heroes. The players are the actors and the GM takes on the job of director, producer, referee and actor for all the other characters within the story. It differs, though, in that the game is open-ended. There is no script! Each game session has an objective but the PCs (and players!) might not know what it is. Once the players know the objective, it is up to them, via their characters, to decide how to accomplish it.