From China Digital Space
Chinese Communist Party. The first character, tǔ 土, can be read as a noun meaning "earth" or "soil," or as an adjective meaning "earthy," "unrefined," or "uncouth."
There is some disagreement about the origin of this term. Some say that TG derives from "Earthy Eighth Route" (Tǔ Bālù 土八路), a nickname for the Chinese communist military brigade during World War II known as the Eighth Route Army. Others believe TG was coined by Chiang Kai-shek to refer to the Chinese Communist Party (CCP) after he and the Nationalists fled to Taiwan. Still others say it was invented in Hong Kong in the 1990s to disparagingly refer to the CCP.
Netizens use "TG" to avoid censorship, though this tactic is not foolproof. (Tǔgòng 土共 is blocked from Weibo search results as of August 27, 2015.) For instance, in April 2015 Weibo user @rifle76 used the term in response to a post about a leaked video of CCTV personality Bi Fujian mocking Mao Zedong. Both the original Weibo post and @rifle76's comment were deleted by Sina, as indicated by FreeWeibo:
@rifle76: To eat TG's food and oppose TG is disloyalty; to be a Chinese person and hold out the TG's rice bowl is an injustice. (April 8, 2015)