An annotation is a note you add to a text to explain something, ask a question, or record your thoughts. When you write in the margins of a book or add a comment to highlight an interesting passage, you're making an annotation.

Students often annotate while reading difficult material. You might underline a confusing sentence and write “What does this mean?” in the margin, or mark an important fact with a star and note “This will be on the test.” Scientists annotate research papers to track important findings. Historians annotate old documents to explain outdated words or provide context about when something was written.

Think of annotations as a conversation between you and the text: the author says something, and your annotation is your response. When you annotate actively, you engage with ideas by questioning them, connecting them to what you know, or marking what matters most. This helps you understand and remember them better.

In digital contexts, you can annotate PDFs, photos, or videos by adding text, arrows, or highlights. A teacher might return an essay covered in annotations pointing out strong arguments or suggesting improvements. Good annotations transform a book from something you merely read into something you've truly wrestled with and made your own.