ORAC is an acronym for "oxygen radical absorbance capacity" which relates to the effects of different foods upon the body.
At one time the USDA gave credence to the idea that foods with a high ORAC value could remove free radicals from the body but has since rescinded on account of a general lack of evidence. The thing is that ORAC only has an observable effect in vitro. Outside of the laboratory, there are too many variables present to conduct a proper experiment.
Whether or not to side with the USDA's original or revised opinion regarding ORAC is up to you. Whether or not "antioxidants" actually do anything positive for your health is still up for debate.
Unsurprisingly, there are a number of dubious companies seeking to capitalize on this craze by marketing products with high ORAC numbers. This includes stuff like Mona Vie juice and similar products.
Foods with a high ORAC value include such "superfoods" as pomegranate, goji berries, pinto beans, chokeberries raw cocoa, blueberries, and purple vegetables.