In statistics, the 68-95-97 rule is known as the three sigma rule or the empirical rule. This rule represents that if there is normal distribution, 68% of the values lie within 1 standard deviation of the mean, 95% of the values lie within 2 standard deviations of the mean, 97% of the values lie within 3 standard deviations of the mean.
The Empirical rule is generally used to give a rough estimate of probability of something given its standard deviation. It is used as test for outliers i.e., to check whether the test identifies with the normality distribution curve and acts as a test for normality. Suppose there are 3 or more standard deviations, there is a reasonable doubt to check the normality of curve before proceeding any further.