자막이 · 자막을
subtitles, captions
Example
한국 드라마를 자막 없이 보고 싶어요.
I want to watch Korean dramas without subtitles.
Word parts
자 letter+막 curtain
Literally 'letter screen' (幕 'curtain, screen').
Good to know
Korean variety shows are famous for colorful on-screen captions, which are also called 자막.
Related words