definition of annotation
An annotation is a metadata (e.g. a comment, explanation, presentational markup) attached to text, image, or other data.
1. annotation-a comment or instruction (usually added); his notes were appended at the end of the article; he added a short notation to the address on the envelope. notation, note. poste restante-a notation written on mail that is to be held at the post office until called for (not in the United States or Canada).