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It means "monetize your webpages" in the sense of "monetize one's webpages".
It's curious that they should do this. Even FastClick pays commission if you refer a new member. Given that AdSense has been running for nearly a year and a half, I would have thought most people who were going to refer people to AdSense as a favour would already have done it.
Hasn't Google got enough advertising from the "Ads by Goooooogle" link? If they toss in a little incentive with this "tell a friend" feature, AdSense would spread like wildfire. or even more so.