What is Precision?

A picture can paint a thousand words, and the following images should help give you a quick mental picture of what is meant by precision.

Precision is a term used to describe data from an experiment that has been repeated several times. If the experiment yields a tightly grouped set of data points, then it has high precision; the greater the scatter of data points, the lower the precision.

To quantify precision, in other words to describe it with a number, scientists use such measures as standard deviation and variance.