It's called tags. Imagine if any post on HN could be tagged by anyone. Then, you are free to only read HN/Europe (all posts tagged Europe). Or browse the regula

It's called tags. Imagine if any post on HN could be tagged by anyone. Then, you are free to only read HN/Europe (all posts tagged Europe). Or browse the regular home page. It won't happen because HN has made a conscious choice of not going after all the "web 2.0" gimmicks, but sometimes you wish it wasn't completely the case.