Mean, median and mode
Mean is the total shared out; median is the middle value in order; mode is the most common.
A worked example
For 3, 5, 6, 8, 40 the mean is 12.4 but the median is 6. One outlier drags the mean up and leaves the median where it was.
The mistake people actually make
When there is an extreme value, the median usually describes a typical case better than the mean.