To start off simply, a visual novel is an interactive fiction game usually with anime style art. Visual novels are quite different from other kinds of games people may be familiar with because of the minimal gameplay. Most of the player's interaction is clicking to move on with the story. Most visual novels have multiples endings and story lines (similar to the Choose Your Own Adventure Books).
An example of a visual novel would be here:
http://www.youtube.com/watch?v=NScZdI2cWkQAnyways, I was thinking of creating of my own visual novel with the Ren'py engine. I don't really know if I'll be able to actually finish creating the whole game, but I'm working on it right now. The game will just be mainly text, with a few choices the player can make.
I'll post a bit about the story in a different journal entry.