The <em>empirical rule </em>states that for a bell shaped distribution, nearly all of the data will fall within three standard deviations of the mean.
<em>Chebyshev’s inequality </em>says that at least of data from a sample will fall within standard deviations from the mean.
We have to remember that Chebyshev’s inequality has been proven mathematically for any distribution. But the empirical rule is a tool created for bell shaped distributions.