MTT Bounty question: What is the diffference between PKO and Bounty Builder?

I noticed these MTT knockout games have different names, but I'm not sure what the difference is structurally between a bounty builder and a progressive knock out.

Both are using 50% of the prize pool towards bounties. And both have half the bounty go to the winner of the pot and half the bounty goes onto the winner's own bounty.

So what is the difference between these two names?