Nominal prices are the actual reported prices of the product. In the nominal price trend graphs, the prices of the product are shown in the dollar value of the year reported. This means that a value shown in 1993 is its value in 1993 dollars and its value shown in 1998 is in 1998 dollars.
Real prices are the prices of the product that take account for increases due to inflation. Real price trends show the prices of the product in today's dollar value. In other words, all of the prices have been adjusted so that they are expressed in current (2007) dollars. This was done using the producer price index for all commodities as reported by the U.S. Bureau of Labor Statistics.