Seth Godin points out that 1/2 of every profession is above the mean and 1/2 are below.

This is only true if the statistical distribution of metric for the profession is symmetric. Then the Mean = Median.

The Median describes the "middle" of the distribution in value terms - 1/2 above, 1/2 below.

The Mean represents the total of all the values divided by the number of values. If skewed, the Mean can be far removed from Median - in either direction.

In the project management domain, this confusion is critical to understanding the probabilistic aspects of duration or cost. The Most Likely value used in PERT and Monte Carlo is the Mean - the value the occurs most often when the task duration or cost is observed a number of times.

Richard Rodger has a small error as well. The item marked Median "could" actually the Mode of the distribution, depending on its shape. The value that occurs most often. The Median is the "middle most" value.