Interactive fiction (IF) is a broad term. Strictly speaking, interactive fiction is anything in which you influence the outcome of a story, like continuous stories you can add to or those old "Choose Your Own Adventure" books with their branching stories. But there is a more specialized meaning of interactive fiction...computer adventure games.
The first computer game was created more than 20 years ago. That means that folks who played them were really ahead of the rest of civilization since personal computers were in their infancy. Some of those guys have been playing for all those years--which means they are uber-nerds.
In general, computer adventure games are computer programs which tell you a story. In them you play a character in the story, and you move the story along through your actions. In many pieces of IF you have to solve puzzles to keep the story going, puzzles like "How do I open the locked door?" or "How can I get the bridle off the alpaca so I can return it to Barry?" In some games you also have to interact with non-player characters (NPCs) to keep the plot unfolding.
Because IF involves storytelling and puzzle-solving, it tends to emphasize thought over action...
So people using their minds to play games? Doesn't sound like they'd hang around MySpace too much. They've probably written the code for something that's way beyond it. Or they taught the founder of MySpace how to do it--while simultaneously writing the latest Mensa test.
IF comes in two flavors: graphic and text. Text adventures came first. Playing them is like reading a book in which you have to type commands to tell the protagonist what to do...Graphic adventures tell their stories through pictures rather than words.
There's an IF archive for text adventures. I tried going there, but it requires more brain power than I have room for.