MFA means Made For Adsense - usually low-quality websites with some content, very clean design and lots of AdSense ads.
Made For Adsense sites is low quality with not any valuable content. they are built by folks to get web visitors to the website for the sole purpose of clicking on advertisements(Specially Adsense ads). The people who are in business of AdSense Arbitrage use MFA sites.
MFA means Masters of Fine Arts .. you can earn a degree in it! Or.. its a Made for Adsense site that has only one purpose, for your vistors to click on the Adsense ads. Wikipedia just calls them scrapper sites here you go: http://en.wikipedia.org/wiki/Scraper_site
Thank you all guys, I also find some one saying G will flag your site as MFA by bounce rate and keywords stuffing, is it true? I know low quality content will result in visitors want leave your site right away, that low PV indicate your sites low quality, so G will count in your PV as a factor of MFA?
If you add unique, useful and fresh content in your site then you do not have to worry about MFA or any other thing.
They are low quality sites with keyword rich content just for Adsense. Better you make MFA's into decent sites with some unique content and you update often