The guy below explained it well, but I'll use an example.
Let's say that I want to link to a specific post on Cake Wrecks.
So it's an Olympic themed post, with things like the one above. If I were to simply link you to http://www.cakewrecks.com you'd get the right post if you looked right away. But tomorrow there will be new Wrecks, because "professional" cake designers screw up constantly. And the Olympics cakes will be on the second page, and in a month they'll be on the 75th.
It's the address of a specific entry in a blog that remains extant even when the comment or blog has been moved to an archive; a permanent link through which the comment can be accessed.
Let's say that I want to link to a specific post on Cake Wrecks.
So it's an Olympic themed post, with things like the one above. If I were to simply link you to http://www.cakewrecks.com you'd get the right post if you looked right away. But tomorrow there will be new Wrecks, because "professional" cake designers screw up constantly. And the Olympics cakes will be on the second page, and in a month they'll be on the 75th.
So instead of linking to the front page, you link to the specific blog post: http://www.cakewrecks.com/hom...
That will take you to the Olympics post whenever you click it, no matter how long has passed.