Definitions:
a very brief period of time

importance

a turning effect produced by a force acting at a distance on an object.

a quantity that expresses the average or expected value of the first, second, third, or fourth power of the deviation of each component of a frequency distribution from a given value, typically mean or zero. the first moment is the mean, the second moment the variance, the third moment the skew, and the fourth moment the kurtosis.