From b2evolution manual
This manual page is outdated. NEW PAGE: Permalink in b2evolution v5+.
Permalink is short for "permanent link". It is a link that readers can use to bookmark or link to a specific blog post. This is important because a blog's front page often changes rapidly and old blog posts often get archived and can be difficult to find. The permalinks assure that your old content can still be found easily by the people who want it.
In b2evolution, permalinks are often found at the very beginning or the very end of each post, often illustrated by a little page icon http://demo.b2evolution.net/HEAD/blogs/skins/custom/img/icon_minipost.gif or a little chain icon http://demo.b2evolution.net/HEAD/blogs/rsc/icons/chain_link.gif.
Information on changing the appearance of permalinks can be found here.