WTF is PLOS
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To elaborate on what ButterflyEffect wrote, it's an open-access journal aiming to make scientific research freely available to the public (as well as change some of the other closed and insular aspects of science).
According to the title of the AMA which this links to and by googling "PLOS", it's the Public Library of Science.
I respect that you didn't resort to http://www.lmgtfy.com/.