What does forged Pagerank mean?

When i was searching for a blog to buy with some pagerank i came across many sites which had 'Forged' Pagerank. What does this forged pagerank mean? What is the difference between a valid pagerank and a forged pagerank?

 

But how are these forged pagerank sites made?

 

Look at the cached version of the page. If it is forged, you'll see the site it is redirecting to, and not the domain itself.

 

Hey, here you can find more details about the forged page rank

 

they are obtained using 301 redirect!!