noun
woman with a nice rear view; good-looking from behind
Colloquial, somewhat dated wasei-eigo from English 'back' and German 'schön'. Refers to a woman whose back view is attractive, often implying the front may not match. Can be used playfully or as mild slang.
from English back · from German schön
あの子、バックシャンだね。
That girl looks great from behind, doesn't she?
バックシャンに期待して声をかけたら、がっかりした。
I approached her expecting a beauty from behind, but was disappointed.