The median is the middle number in a data set when all the data has been arranged in ascending order. If there are an odd number of numbers involved, then the median is easy to find. If there are an even number of numbers involved, then the median is the average of the two numbers in the middle.

For example, the median of the set {1, 2, 3} is 2, while the median of the set {1, 2, 3, 4} is 2.5.