From China Digital Space
Ancient name for China; sarcastic nickname for the current party-state.
Using the historic term "Celestial Empire" suggests that China's leaders are self-important, have a China-centric view of the world, and embody many of the imperial trappings communism was supposed to have cast off.
Zhenshidehuangyane (@真实的谎言e): Special characteristics of the Celestial Empire: corruption is its father, shamelessness is its mother! What a mystical country! (September 24, 2014)
天朝特色，腐败是爹，无耻是妈！ //@老王故事会://@相思洋: 神奇的国度！[Chinese]
"Celestial Empire" is used plays on words, such as Celestial Empire goes into the pot, a near-homonym for "Celestial Empire above all other nations."
Since "Celestial Empire" is often used in criticism of the government or state of affairs in China, an alternate way of writing it has at times been blocked from Sina Weibo search results.
TG is sometimes used as an approximate abbreviation, but it actually stands for Tǔgòng 土共, another name for the Communist Party of China.