annotation

an·no·ta·tion  (n-tshn)

n.

1. The act or process of furnishing critical commentary or explanatory notes.

2. A critical or explanatory note; a commentary.

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A marking placed on imagery or drawings for explanatory purposes or to indicate items or areas of special importance.

Thesaurus

Noun	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) commentary, comment - a written explanation or criticism or illustration that is added to a book or other textual material; "he wrote an extended comment on the proposal" cite, quotation, reference, mention, acknowledgment, citation, credit - a short note recognizing a source of information or of a quoted passage; "the student's essay failed to list several important citations"; "the acknowledgments are usually printed at the front of a book"; "the article includes mention of similar clinical cases" footnote, footer - a printed note placed below the text on a printed page N.B., nota bene, NB - a Latin phrase (or its abbreviation) used to indicate that special attention should be paid to something; "the margins of his book were generously supplied with pencilled NBs" postscript, PS - a note appended to a letter after the signature
	2.	annotation - the act of adding notes annotating expanding upon, expansion - adding information or detail

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annotation

noun note, comment, explanation, observation, interpretation, illustration, commentary, gloss, footnote, exegesis, explication, elucidation