Refers to a web site, often made by an angst-ridden teenager, containing mostly ramblings about life's little foibles. Can also contain bad teen-age poetry. Known for gratuitous use of excessively dark or pale color schemes, and lowercase letters all over the place.
Most e/n sites are blog sites, with a lot of microcontent. Places like LiveJournal and Blogger let users make small updates easily, generating all the HTML and transferring the files automatically. LiveJournal even lets visitors leave comments on each entry, in a vaguely Slash-like way.
Most e/n sites are boring if not depressing; they make up a fair amount of the entries on losers.org. Very little of the content is actually of any interest to the outside world. In response to a Slashdot troll who was dogging a user about his e/n site, the user replied "My web site is not for you. It is for me." That was one of very few instances where a troll has been left speechless.
According to The Automatic E/N Web Site (http://www.conhugeco.org/en/), E/N can stand for "Eternal/Noise", "Everything/Nothing", "Endless/Nonsense", or something else.
Update Jan 28 2004: In the years since I originally noded this, the term "e/n site" has been shunned by the public in favor of more specific terms like "blog" and "LiveJournal."