I'm not familiar with that
App, so can't exactly describe the context it's being used in, but standard deviation is a statistical term that indicates how far a value deviates or varies from the mean (average) for that value over a sample data set. A lower standard deviation means the values are closer to the mean (
expected value) indicating lower variance, while a higher one means they're spread out farther away from the mean indicating higher variance. So it's useful in describing variance, and is calculated as the square root of the variance of the sample.