Permalink is short for "permanent link".
A permalink is a link that readers can use to bookmark or link to a specific 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 to refer to it.
In b2evolution evoSkins, permalinks are often found at the very beginning or the very end of each post, often illustrated by a little page icon or a little chain icon.
Information on changing the appearance of permalinks can be found in How to Change the Appearance of my Permalinks.