The term closed captioning refers to the synchronized display of the text of a translation or transcription of the dialogue or audio track at the bottom of the screen during the scenes when sound is unavailable or not clearly audible.
The term "closed" (versus "open") indicates that the captions are not visible until activated by the viewer, usually via the remote control or menu option. On the other hand, "open", "burned-in", "baked on", "hard-coded", or simply "hard" captions 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. "Subtitles" assume the viewer can hear but cannot understand the language or accent, or the speech is not entirely clear, so they transcribe only 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. Also, the term closed caption has come to be used to also refer to the North American EIA-608 encoding that is used with NTSC-compatible video.
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), which is why the term subtitle is also used to refer to the Ceefax-based Teletext encoding that is used with PAL-compatible video. The term subtitle has been replaced with the caption in a number of markets — such as Australia and New Zealand — that purchase large amounts of imported US material, with much of that video having had the US CC logo already superimposed over the start of it. In New Zealand, broadcasters superimpose an ear logo with a line through it that represents subtitles for the hard of hearing, even though they are currently referred to as captions. In the UK, modern digital television services have subtitles for the majority of programs, so it is no longer necessary to highlight which have to caption and which do not.
Remote control handsets for TVs, DVDs, and similar devices in most European markets often use "SUB" or "SUBTITLE" on the button used to control the display of subtitles/captions.
Closed captioning and subtitling are both processes of displaying text to provide additional or interpretive information. Both are typically used as a transcription of the audio portion of a program as it occurs (either verbatim or in edited form), sometimes including descriptions of non-speech elements. Other uses have been to provide a textual alternative language translation of a presentation's primary audio language that is usually burned-in (or "open") to the video and unselectable. HTML5 defines subtitles as a "transcription or translation of the dialogue ... when sound is available but not understood" by the viewer (for example, dialogue in a foreign language) and captions as a "transcription or translation of the dialogue, sound effects, relevant musical cues, and other relevant audio information ... when sound is unavailable or not clearly audible" (for example, when audio is muted or the viewer is deaf or hard of hearing).