It stands for Bisphenol A. It is a chemical used in the production of plastics and resins, such as some water bottles and the coatings of some food cans. It is also used in some consumer goods, such as compact discs and thermal cash register tapes. And it has generated controversy about its impact on human health and development.
Here is another trendy research topic. A lot of health & fitness magazines warn against using water bottles with BPA. Pretty much this article says the FDA has decided the current research doesn’t warrant the omgdeathBPA concerns, but better safe than sorry.