Accuracy and Precision
Accuracy refers to the closeness between measurements (observations) and their expectations ("true" values). The farther a measurement is from its expected value, the less accurate it is.
Precision pertains to the closeness to one another of a set of repeated observations of a random variable. Thus, if such observations are closely clustered together, then these observations are considered to have been obtained with high precision.
The example and the previous definitions are presented here to clarify some key terms necessary for communicating, integrating, or analyzing any set of measurements. A full understanding of these concepts requires a strong background in statistics.