dianebrewster Very clear description of the differences, but can I just be a little bit nitpick-y about one point:-
If we are told the average wage, in an industry, is £50k because they are using mean average and include the v high earners, that's quite different to finding out most employees are actually on £30k - modal average.
In most statistics you see about wages, for example from the ONS, it's actually the median that is given.
The reason that the mode isn't used particularly for wages is that the mode for wages will usually be very much lower than the median.
This is a chart from the ONS of distribution of hourly earnings for all employees in the UK.
You'll see that the largest number (ie the mode) is right down at the minimum wage level.
The median hourly earnings for all employees (full time and part time) was £13.24 and for full time only was £15.68.
So you can see that from that chart there is a big difference between mode - which is minimum wage - and median which is £13.24 for all employees.