permalink

Permalink is short for "permanent link". While the front page of your blog only shows the latest posts, a permalink points to a particular post. This link will always be a valid link directly to the post, unless the post is deleted. Therefore if you want to link to a post in somebody else's blog you should always use the permalink.
These types of links are commonly used in blog sites because entries in blogs have variable addresses that are updated and frequently changed. Permalinks give a specific web address to a blog entry so that they can be bookmarked by a visitor for further reference; or that they can be linked to from other websites.
Read more on this site: http://mail2web.com/blog/2010/04/permalink/