What's the meaning of AdSense for Content Host

Now have 6 different labels in Adsense Property info

[Olney]

I just checked my Adsense account.
I've never noticed this before & I believe I've looked recently.
Anyone have a clue to what all of these are for (especially host) in the "property info" portion of your account settings

AdSense for Content: ca-pub-#*$!#*$!#*$!#*$!#*$!XX
AdSense for Content Host: ca-#*$!#*$!#*$!#*$!#*$!XX
AdSense for Search: partner-pub-#*$!#*$!#*$!#*$!#*$!XX
AdSense for Search Host: partner-pub-#*$!#*$!#*$!#*$!#*$!XX
Referrals: ca-ref-pub-#*$!#*$!#*$!#*$!#*$!XX
Referrals Host: ca-ref-pub-#*$!#*$!#*$!#*$!#*$!XX

Is it old I just haven't noticed it?

[drall]

I noticed that last night also, the other parts have always been there for us except the "host" which is new and I have no idea what it stands for.

[timwestla]

AdSense for Search has quite a few more options now. I imagine it has something to do with that.

[jason207]

host_id is also a var in the adsense API code in addition to the client_id, so adsense knows to pay both parties. it may just be releated to that..

[AdSenseAdvisor]

Our AdSense API team tells me that the AdSense Host properties that some publishers are seeing in their accounts are being shown in error. These ID numbers are are used for websites that have implemented the AdSense API ([code.google.com ]).

Our engineering teams are working to investigate and resolve the issue. In the meantime, know that there have been no actual changes to the affected accounts, and no action is needed on your part. Sorry for any confusion.

-ASA