Annotation refers to the act of adding notes, comments, or explanations to a text, image, or document. It is a way of providing additional information or clarifying certain points within the original content. Full definition
The drawings in the exhibition date from 1966 and consist of annotations of ideas for works, some of which were never realized. (artzine.com)
Henri Cartier - Bresson Cuba, 1934 Gelatin silver print; printed c. 1934 6 1/2 x 9 5/8 inches Signed, titled and dated with annotations in pencil on print verso. (howardgreenberg.com)
I am however satisfied with the functionality of the pen for making annotations on the pdfs. (goodereader.com)