The median of a set of quantitative data (a set of numbers) is the middle number when the measurements are arranged in ascending or descending order.
Suppose we have a data set containing n values. To calculate the median we arrange the measurements from smallest to largest.
- If n is odd, the median is the middle number.
- If n is even, the median is the average (or mean) of the middle two numbers.

The median is said to be a resistant measure of central tendency, meaning it isn't affected by outliers.
-- ErinEsp - 24 May 2010