From China Digital Space
草泥马 (cǎonímǎ): grass-mud horse
Grass-mud horse, which sounds nearly the same in Chinese as “f*** your mother” (cào nǐ mā), was created as a way to get around and poke fun at government censorship of vulgar content. The idea caught fire after netizens made a video depicting the grass-mud horse at war with and eventually defeating the river crab (河蟹 héxiè), a homonym for the propaganda catchword “harmony” (和谐 héxié). Netizens continually expanded the lore of the grass-mud horse by creating catchy songs and fake nature documentaries on YouTube and other video sharing sites.
The phrase is especially meaningful on a political level because the Communist Party is often described as “the mother” of the people--“f*** your mother” can also suggest “f*** the Party.” The grass-mud horse is one of many mythical creatures created by netizens in response to increasingly strict censorship measures.
The term has since developed an additional meaning: a “grass-mud horse” is someone who is web-savvy and critical of government attempts at censorship. As one Chinese blogger explains, “‘Grass-Mud Horse’ represents information and opinions that cannot be accepted by the mainstream discourse, and ‘The Song of the Grass Mud Horse’ has become a metaphor of the power struggle over Internet expression.”