What is closed or open captioning?
Closed captioning are subtitles specifically intended for people who are hearing impaired or deaf. The captions or subtitles are called closed captions because they are hidden, until they are otherwise 'opened' by the viewer from a menu or by selecting the relevant option from their TV settings. Closed captioning tends to be a transcription rather than a translation, and usually contain descriptions of important non-dialog audio such as "sighs" or "music".
Open captioning or subtitles are an integral part of the film/video and can't be closed off from view. Subtitles are used to translate dialog from a foreign/source language to the target (native language) of the audience.