A standard deviation is a statistic that measures the disperion of a data set relative to its mean.
If the standard deviation is less that's mean there is lesser change that the actual return will be ways from the expected return.
A low standard deviation indicates that the data points tend to be very close to the mean; a high standard deviation indicates that the data points are spread out over a large range of values. A useful property of standard deviation is that, unlike variance, it is expressed in the same units as the data.