What is an RPG?

It is a perfectly valid question.  I really didn't know myself until recently.  The acronym stands for Role Playing Game.  Each participant takes a character (or characters) and writes for them.  It's a lot like fanfic, but no one author has complete control over what happens.  Basically, that's it.  There are different variations on the idea, some people use dice to determine what happens, some make you measure out numerically a character's strengths and weakness, some put one person in overriding control, but it all comes back to the same basic concept.