Originally slang terms used to identify a group of human derived sophonts claiming relatively pure ancestry of Earth Chinese origin.
During the Federation period the term came to refer to non-Penglaiese (unlike the Penglaiese they still called themselves Chinese) Sol System baseline or near-baseline asiatics, specifically Mandarin or more often Cantonese speakers who managed to make it through the dark age. They already had a strong cis-lunar orbital presence and good blue goo, and had the resources to take some of those Chinese following the Great Expulsion.
Many of the pure-genome Chin eventually made it to Atlantis, which was close and resource rich, with a flourishing economy. They soon established themselves as traders and merchants, eventually spreading throughout most of the NoCoZo. One identifying characteristic was their ability to speak Anglic, Mandarin and Cantonese, three of the source languages of Chinglish.
While very few recognizable baseline or nearbaseline asiatics remain (apart from novelty lazurogenics), there are still a few purists (House Chin) who, as with House Stevens, are intent on retaining the original genome.