The tl;dr version: E-poetry is poetry that arises from an engagement with the possibilities offered by digital media. This site is full of examples, but here’s a simple one: “Puddle” by Neil Hennessy.
Now try printing it out. 🙂
For a more detailed response, I will reference my “Digital Poetry” entry for the Johns Hopkins Guide to Digital Media which I begin by discussing what e-poetry is, and what it isn’t.