Third Sector

Sometimes called the Voluntary Sector or non-profit, the term seems to be a
child of the 1970s. The idea itself rather than the term is hundreds, possibly
thousands of years old.

See also http://en.wikipedia.org/wiki/Third_Sector
http://books.google.com/ngrams/graph?content=Third+Sector&year_start=1950&year_end=2008&corpus=15&smoothing=0&share=