da4-zi4-bao4, according to schist.
The medium of choice for propaganda and debate by Chinese people leading into the Great Proletarian Cultural Revolution. Messages would be written on large sheets of paper, then pasted to walls in public places -- usually on top of previous big character posters.
One of the most important posters was that of Nie Yuanzi, a Beijing University philosophy teacher, who
described the counter-revolutionary "crimes" of the University administration and fellow teachers. At the time (early 1966), describing someone as "counter-revolutionary," "rightist," or "revisionist" was not a literal acusation of such political beliefs but essentially a declaration of dislike for the target. While this began to cause a stir in the Beijing community, Chairman Mao Zedong ordered that the text of the poster be reprinted in China's main newspaper, People's Daily. As the message spread, backed by the "support" of Chairman Mao, the claim of a school administration being counter-revolutionary was all the necessary justification for rebellion. Students everywhere began overthrowing their educational cadres, despite attempts at intervention by Liu Shaoqi. Nie's poster became the spark that ignited the Cultural Revolution.
The other major Big Character Poster, "Bombard the Headquarters," was written that summer by Mao Zedong himself. While the Chinese Communist Party attempted to curb the chaos that had ignited in the schools, Mao fanned the flames with his broad and generalized statements to the students that "to rebel is justified." He also provided a description of how to organize -- laying the groundwork for what would become the Red Guard.