I guess they use advertising on the web page to pay for grains of rice. For every word you correctly define, you earn 10 grains of rice to feed the hungry through the United Nations. Here is a quote from the FAQ page
"The rice is distributed by the United Nations World Food Program (WFP). The World Food Program is the world’s largest food aid agency, working with over 1,000 other organizations in over 75 countries. In addition to providing food, the World Food Program helps hungry people to become self-reliant so that they escape hunger for good. Wherever possible, the World Food Program buys food locally to support local farmers and the local economy. We encourage you to visit the United Nations World Food Program to learn more about their successful approach to ending hunger."
Seems like a good plan, right? Well here's the thing. I counted 10 grains of cooked rice out, its like reaching into the bowl and taking a pinch...a small pinch. Thats 10 grains. I googled it, and apparently a cup of uncooked long grain rice has about 7250 grains. 1 cup of uncooked rice makes about 2 cups of cooked rice, but still, thats a lot of words to define!
Its actually really fun though, there are a few I don't know, and some that you can guess based on the root word. Try it out.