a couple where both spouses are not Hong Kong citizens
Definitions (粵典–words.hk)
名詞、香港
父母都唔係香港居民而喺香港所生嘅子女 children born locally whose parents are non-permanent residents of Hong Kong; literally: doubly non-permanent resident (children)
香港而家好多雙非兒童。
香港而家好多双非儿童。
hoeng1 gong2 ji4 gaa1 hou2 do1 soeng1 fei1 ji4 tung4. There are many doubly non-permanent resident children in Hong Kong nowadays.
Definitions (Wiktionary)
noun, Hong-Kong
a pair of parents who are both Mainlanders, and/or their children (anchor babies)