Standard deviation is a method of plotting variations from an average figure. To plot a standard deviation, a population of values is added together and divided by the number of values to produce an average. the difference between the individual values is then calculated and squared. the square root of the added deviation values divided by the number of values is the standard deviation. Standard deviations can be used for plotting anomalies in statistical research as well is creating reliable behavioral indicators for statistical values. Applications of this methodology include scientific research, industrial quality control and demographics. 
Examples of Standard Deviation:
http://en.wikipedia.org/wiki/Standard_deviation#Basic_examples http://www.une.edu.au/WebStat/unit_materials/c4_descriptive_statistics/standard_deviation.htm 
A plot of a normal distribution (or bell curve). Each colored band has a width of one standard deviation. 
Cumulative probability of a normal distribution with expected value 0 and standard deviation 1. 
