Standard deviation is a measure of how spread out data values are from their average value. It tells us how much variation or dispersion there is in a set of data. The higher the standard deviation, the more spread out the data values are from the mean (average). In other words, it measures how much the data deviates from its average value.
For example, if we have a dataset with an average height of 5'10" and a standard deviation of 2 inches, this means that most people in the dataset fall within two inches above or below their average height (i.e., between 5'9"8 and 5'11"). However, some people may be taller than 6 feet or shorter than 4 feet with relatively low probability.
In summary, standard deviation is a measure of how spread out data values are from the mean, which can help us understand the variability in a dataset.