1. The act of adding notes
   "The students spent hours annotating their textbooks to prepare for the exam";
   - annotation

1. Add explanatory notes to or supply with critical comments
   "The scholar annotated the early edition of a famous novel";
   - footnote
    
2. Provide interlinear explanations for words or phrases
   "He annotated on what his teacher had written";
   - gloss, comment

Type of: compose, expanding upon, expansion, indite [archaic], interpret, pen, rede [archaic], write

Encyclopedia: Annotating