Mean is the average value. It is sensitive to extreme values but is easy to be managed mathematically.

Example 1

For the dataset: 2, 6, 13, 17, 22, the mean is 60/5 = 12.

Example 2

For the dataset: 2, 6, 13, 17, 22, 900, the mean is 960/6 = 160. Note the influence of the outlier 900 to the mean is large.