They are links that stay on other sites permantly. This way you can have links to your domain name with keywords that you know will be around for a long time. The more links pointing to your site the more it helps in search engines and traffic if the links are from sites that are related to your topic or same topic.
when you post an article on a blog, the blogpost stays on the main index page for a while but also shows under the category page and pages where they are tagged. but that blogpost has its own URL where the post can be found directly. that direct link to the blogpost is called permalink
My blog PR3 become PR0 after I delete Uncategory list. I've made Uncategory list again but my blog still zero.... This is because permalink or what?