Terminology
The term "closed" in closed captioning indicates that not all viewers see the captions—only those who choose to decode or activate them. This distinguishes from "open captions" (sometimes called "burned-in" or "hardcoded" captions), which are visible to all viewers.
Most of the world does not distinguish captions from subtitles. In the United States and Canada, these terms do have different meanings, however: "subtitles" assume the viewer can hear but cannot understand the language or accent, or the speech is not entirely clear, so they only transcribe dialogue and some on-screen text. "Captions" aim to describe to the deaf and hard of hearing all significant audio content—spoken dialogue and non-speech information such as the identity of speakers and, occasionally, their manner of speaking—along with any significant music or sound effects using words or symbols.
The United Kingdom, Ireland, and most other countries do not distinguish between subtitles and closed captions, and use "subtitles" as the general term—the equivalent of "captioning" is usually referred to as "Subtitles for the hard of hearing". Their presence is referenced on screen by notation which says "Subtitles", or previously "Subtitles 888" or just "888" (the latter two are in reference to the conventional teletext channel for captions).
Read more about this topic: Closed Captioning