Unfortunately the terms "captions" and "subtitles" are often used interchangeably. At a quick glance, closed captions and subtitles appear similar. However, they are designed for two different purposes.

Subtitles

Subtitles provide a text alternative, often in a different language, for the dialogue of video footage – the spoken words of characters, narrators and other vocal participants. Essentially, subtitles assume an audience can hear the audio, but need the dialogue provided in text form as well.

Movie subtitled in Chinese and in English, "You have missed this."

Closed Captions

Closed captions, on the other hand, not only supplement for dialogue but other relevant parts of the soundtrack – describing background noises, phones ringing and other audio cues that need describing. Closed captioning assumes an audience cannot hear the audio and needs a text description of what they would otherwise be hearing.

Saturday Night Live episode closed caption, "And Raised. [Cheers and applause.] "