A digital garden is like an ever-growing blog.
This is a beautiful explanation by Maggie Appleton of the concept, as well as the history, of Digital Gardening.
My favorite part about having a digital garden is that I'm more likely to start something if I don't feel obligated to finish and polish it immediately. If something begins to interest me and I want to write and learn about it, all I need to do here is get the ball rolling.