From China Digital Space
TG are the initials for 土共 (tǔgòng), another name for the Communist Party of China.
The term is made of two characters, 土 meaning, “land; dirt; base; unrefined; or local” and 共 meaning “public or common.” (The character 共 is also in the Chinese word for Communism, 共产主义.) There is some disagreement about the origin of the term. Some say that the term comes from 土八路 which is a nickname for 八路军, the Eight Route Army. The Eighth Route Army was the larger of the two major Chinese communist forces which fought the Japanese from 1937 to 1945. Others say that the term was created by Chiang Kai-shek to refer to the Party after he fled to Taiwan. Still others say the term was invented in the 90s by people living in Hong Kong to sarcastically refer to the party. Because the term means different things to different people, one has to pay attention to context to determine if it is used sarcastically or positively. When used sarcastically, netizens point out that TG are also the initials for 贪官 (tānguān) meaning “corrupt official.”
TG can also stand for 天国 (tiānguó) which means the same thing as Celestial Empire.
TG, in Chinese slang can also refer to the English word “transgender.”