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Enlightenment period (late 19th to early 20th century)
Example
개화기에는 신문과 전차 같은 새로운 문물이 들어왔어요.
During the Enlightenment period, new things like newspapers and streetcars arrived.
Word parts
개 open+화 change+기 period
Literally 'enlightenment period', roughly the 1870s to 1910.