An annotation is a special kind of note-taking directly on a piece of writing or text, usually in the margins of the page. The purpose of annotating is to aid your understanding of the text, engage in a conversation with the author of the text, and provide you with a reminder of your reading experience when you return to the text. When you annotate, you jot down quick summaries, questions, or observations in the margins, and underline, highlight, or comment on the text itself. Annotations can also be made using sticky notes (paper or digital) and the insert-comment feature of word-processing software.

The annotations in an annotated bibliography are somewhat different from annotations as defined above. An annotated bibliography is a list of your research sources (called a Works Cited in MLA format) with a paragraph or more of annotation—usually a paragraph-length summary and explanation—beneath each source.