Loosely, a unit system defining all magnitudes of units in multiples of ten. The standard for the MetricSystem is known as SI, an abbreviation for Système International d'unités. A quick breakdown of the units may be informative.
There is a ReligiousWar over which should be used, but clearly(!) that should be the MetricSystem. Even the most devout followers of the ImperialSystem rarely deny that the MetricSystem is better.