One of the political movements under the communist government in China. Communists are "left-wing," and this was apparently an attempt at purging "rightist" or anti-communist elements in the general populace. Being labeled a "rightist" was a sort of social death penalty during these times. Rightists could be sent to the countryside for "re-education."
For a more informed summary, read about the Chinese Cultural Revolution.
wikipedia.org dumped 2003-03-17 with terodump