The new tab is for "Negative Keywords" and reportedly "will come up with potential negative keywords for your campaign."
I hope to obtain a screen capture from the member who reported it and post it here, I will update this post if I get it.
The first feedback is:
What I really had hoped it would allow me to do is to use negative keywords right in the Keyword Variations tab, i.e., tell it I was targeting, say, [card games] and then add [-pokemon].
Forum discussion at WebmasterWorld.
Update: Here is the screen capture from "Winooski", a longtime WebmasterWorld user, thank you:
Full size screen capture here.