The median of a data set is the value above which half of the data lie and below which half the data lie. It is considered to be the "middle" number of the data set. If the data set is composed of an odd number of entries, the median is the exact middle number. If the data set is composed of an even number of entries, the median is the average of the two middle numbers. The median may not be a number in the data set. The median is influenced very little by extreme data values. When computing the median, the data list must be ordered from lowest number to highest number.

The following data set is odd: 1, 2, 5, 7, 9. The median here is 5, because 5 is the absolute middle number (there are two numbers on either side of it). The following data set is even: 1, 2, 5, 7, 9, 10. Here the median is 6; 5 + 7 (the two numbers in the middle) ÷ 2 = 6.

The median of a data set is a measure of central tendency, like the mean and the mode. It describes the distribution or gives a summary of events that take place in a data set. It can be used for comparison purposes.

The median of a triangle is a segment from a vertex in the triangle to the midpoint of the opposite side. Every triangle has three possible medians--one from each vertex. The centroid is the place inside the triangle where all three medians intersect. This is considered to be the balance point of the triangle.