synchronized visual and/or text alternative for both speech and non-speech audio information needed to understand the media content

Captions are similar to dialogue-only subtitles except captions convey not only the content of spoken dialogue, but also equivalents for non-dialogue audio information needed to understand the program content, including sound effects, music, laughter, speaker identification and location.

Closed Captions are equivalents that can be turned on and off with some players.

Open Captions are any captions that cannot be turned off. For example, if the captions are visual equivalent images of text embedded in video.

Captions should not obscure or obstruct relevant information in the video.

In some countries, captions are called subtitles.

Audio descriptions can be, but do not need to be, captioned since they are descriptions of information that is already presented visually.