When you annotate, you write critical explanations to add extra insight about something. These explanations can be necessary to understanding writings in which the language might be difficult to make sense of without clarification.
The heart of the word annotate is the word note. The Latin annotātus means "noted down," making the word a breeze to remember. A writer will annotate parts that need extra explanation in technical works or classic writings in which the language or concepts might be difficult to grasp. In fact, some works, like James Joyce’s "Ulysses," have entire separate volumes of annotations, and readers must shift back and forth from the novel to the annotations. Now that's a dedicated reader!