@tintin,
"Income averaging" is a very specific tax term. What this means is that if someone has a year with highly unusual income that instead of paying all that tax to the government in one year, they can average the income from three years and pay on the average amount each year. But to qualify, that high income year must be more than 40% higher than the average of the three.
Example. In year one, you make $80,000. In year two, you make $80,000. In year three you make $140,000. The average of these three is $100,000. The high year ($140,000) is 140% of the average, so you could choose to pay taxes on $100,000 each year instead of $80K/$80K/$140K. This might save you money.