I met the Empirical Rule concept in Kehan Academy, and after google it, I found in statistics, it also known as 68-95-99.7 rule or three-sigma rule, following is from wikipedia:

In statistics, the 68–95–99.7 rule, also known as the three-sigma rule or empirical rule, states that nearly all values lie within 3 standard deviations of the mean in a normal distribution.
About 68.27% of the values lie within 1 standard deviation of the mean. Similarly, about 95.45% of the values lie within 2 standard deviations of the mean. Nearly all (99.73%) of the values lie within 3 standard deviations of the mean.

Following is the Youtube video I think is very intuitively:

ck12.org Normal Distribution Problems: Empirical Rule:

ck12.org Exercise: Standard Normal Distribution and the Empirical Rule

Empirical Rule

Empirical Rule Demonstration

The Normal Distribution and the 68-95-99.7 Rule

Empirical Rule In 5 Minutes

Posted by 52nlp