For a random variable X with standard deviation σ‎ and mean μ‎, then $\text{Pr}\left\{|\mathrm{|X}-\mu ||>k\sigma \right\}\le 1/k^2$. While the inequality is a rather weak statement, in that most distributions do not come close to the limit specified, it can be very useful to be able to identify an upper limit that it is impossible for a probability to exceed.