[benregenspan]

That's the definition of a bounce. A visitor comes, they check out one page, they don't interact with anything (reading is not interaction), they leave. This might not be the most useful thing to know for many sites (a simple blog which doesn't have "recirculation" modules / isn't, like larger media sites, geared to having someone come and stay), but it certainly is a useful concept for media sites where pageviews are still king.

But even on a simple blog, bounce rate is a useful stat. Many bloggers don't just want people to come from Hacker News and stay for one article, they want these visitors to click around to related entries after they are done reading. Bounce rate gives a good idea of whether this is happening or not (unless you automatically count almost all visits as non-bounce by triggering an event after a brief time interval).