The median is the middle number in a sequence of numbers. It is used to avoid the problems that occur when an extreme value has a pronounced effect on the mean, sometimes a middle or center of a set of data is used. This is the value of the middle item or, the mean of the values of the two middle items when the data are arranged in an increasing or decreasing order of magnitude.

If you have an odd number of items there is always a middle item whose value serves as the median. If there is an even number of items, the median is determined as the mean of the values of the two middle numbers.

 Mean and media do not always coincide. The median divides the data so that half of the items are less than or equal to the median, while the values of the other half are greater than or equal to the median.

The median is not easily affected by extreme values and can be used to define the middle of a number of objects, properties, or qualities which do not permit a quantitative description.

In issues of inference (estimation, prediction, etc.,) the mean is usually more reliable than the median because the median is subject to greater chance fluctuations than the mean.

The median is also referred to as the 'midpoint.'

For more information, visit this excellent site: http://mathworld.wolfram.com/Median.html