Audio description adds spoken information about important visual details that might not be clear from the main soundtrack alone. It is usually provided through an available alternative audio arrangement or track. The source must supply it and the player must expose it; a general audio-language menu does not guarantee that descriptive narration exists.
A practical example
A viewer may select an audio option that describes actions during gaps in dialogue. Another programme in the same app may have no descriptive track, even when both offer the same spoken language in their ordinary audio selection menus.
A common misunderstanding
Do not label a commentary track or translated dialogue as audio description without checking its actual purpose. Accessibility depends on the content of the track, not merely its language name.
Related terms
Stable technical definition. Editorial approach