What is Annotation?

Legal Definition
An annotation is a metadata (e.g. a comment, explanation, presentational markup) attached to text, image, or other data. Often, annotations make reference to a specific part of the original data.
-- Wikipedia
Legal Definition
Civil law. The designation of a place of deportation. Dig. 32, 1, 3 or the summoning of an, absentee. Dig. lib. 5.

2. In another sense, annotations were the answers of the prince to questions put to him by private persons respecting some doubtful point of law. See Rescript.
-- Bouviers Law Dictionary
Legal Definition
A remark, note or commentary on some passage of a book, intended to illustrate its meaning. Webster. In the civil law. An imperial rescript signed by the emperor. The answers of the prince to questions put to him by private persons respecting some doubtful point of law. Summoning an absentee. Dig. 1, 5. The designation of a place of deportation. Dig. 32, 1, 3.
-- Black's Law Dictionary