A rakushu (a satirical poem with a 31 syllable verse) is a vehicle of expression which was prevalent from the Heian to the Edo period.
In public places, especially intersections and riversides where people easily gathered, notices would be put up, publishing anonymously written kyoka (lit. mad poems) that generally satirized current events. That there was no freedom of speech in those days was a matter of course, and political criticism was a highly risky act. Any literate person, however, could freely engage in discursive activities by anonymously publishing their political views.
"Rakusho" (parodies) were similar in nature with slightly longer passages than those in rakushu. A famous rakusho is the 'Nijo Kawara no Rakusho' (Parody on the riverside of the Nijo-gawa River).