It is when someone exercises or diets excessively in order to be able to "conserve" their caloric intake for alcohol. It can be potentially lethal. It's also the new big problem for women.
http://www.tandfonline.com/doi/full/10.1080/07448481.2011.587487
http://www.tandfonline.com/doi/full/10.1080/07448481.2011.587487