freejung - 3:43 pm on Feb 15, 2011 (gmt 0)
He did, however, say something about the algo "flagging" things as spam. My guess would be that there are specific subroutines in the algo which attempt to detect violations of Google guidelines and reduce the ranking of those pages to below where the relevance portions of the algorithm would normally rank them.
I think that's what we usually refer to as a "filter," whereas we would normally use the word "penalty" to refer to a manually applied penalty.
Both should be distinguished from a loss of rankings due to the relevance portions of the algo simply deciding that your site is no longer as relevant as it used to be. That could be caused by changes in the algo, changes on your site, or changes in the web graph around your site.
I think it's particularly interesting (and encouraging) that he says that if you modify your site such that you are no longer tripping the filter, you should go back to being ranked normally according to your relevance.