standard deviation

Standard deviation is a way of measuring how spread out numbers are in a group of numbers. Imagine you have a group of 10 apples and you want to measure how spread out they are - maybe some are very small, while others are very big. The standard deviation will tell you how big the difference is between the big apples and the small ones. In other words, standard deviation is like a measurement of how different all the apples are from each other.