The Court of Pie Powder was a special court which sat in medieval times during fairs and markets. The purpose of the court was to settle disputes between merchants and customers as well as dealing with acts of theft and violence.
It was said to be the lowest and at the same time most expeditious court in England. It was a very summary court of justice as it had to deal with people who came from afar to attend the fair.It was not unusual for the transgressor to be arrested, tried and judgement given in the space of one hour.
The name may derive from pieds poudrés (dusty feet). So called because justice was done as speedily as dust can fall from the feet.
Or perhaps more likely from the old French word for a pedlar, pied puldreaux
The Court of Pie Powder eventually fell into disuse; the last one convened in 1858, and was finally abolished by statute in 1971
Sources: http://www.yale.edu/lawweb/avalon/blackstone/bk3ch4.htm