IPA: /ˈsuːpərˌtaɪtəl/
KK: /ˈsuːpərˌtaɪtəl/
A written translation of the words spoken or sung in a performance, displayed on a screen above the stage.
The audience could follow the opera easily thanks to the supertitles that translated the lyrics into English.
Supertitle is formed from "super-" (meaning above or over) and "title" (from Latin "titulus", meaning inscription or label). The word refers to a title or label that is displayed above something, such as subtitles in a performance.
Think of something that is 'above' ('super-') a label or name ('title') — that's why a supertitle is a title displayed above.