caption

Short definition from Wiktionary

Noun

1. 1
   The descriptive heading or title, of a document or part thereof.
2. 2
   A title or brief explanation attached to an illustration, cartoon, user interface element, etc.
3. 3
   A piece of text appearing on screen as a subtitle or other part of a film or broadcast, describing dialogue (and sometimes other sound) for viewers who cannot hear.
4. 4
   The section on an official paper (for example, as part of a seizure or capture) that describes when, where, and what was taken, found or executed, and who authorized the act.
5. 5
   A seizure or capture, especially of tangible property (chattel).
6. 6
   A story that is embedded in a pre-existing image (sometimes with image manipulation)

Verb

1. 1
   To add captions to a text or illustration.
2. 2
   To add captions to a film or broadcast.