No argument that the metric system is the most widely used, but outside the US the SAE system is known as the Imperial System. Essentially the same system, I think, but "imperial" probably refers to the British Empire.
When I was first introduced to decimals (at about age 9 or 10) or teacher tried to ease the pain by telling us that we were learning "American arithmetic". Now we, in Oz, are completely metric while the US struggles along with the much clumsier SAE.
These are the USA system of measurement and Imperial system of measurement. The two terms are at time confusing and either is often used to refer to the other. The well main measuring system that had been in use since 1795 and originated fro France was metric measuring system. For more information see http://en.wikipedia.org/wiki/Systems_of_measurement#Metric_system