"An annotated bibliography is a list of citations to books, articles, and documents. Each citation is followed by a brief (usually about 150 works) descriptive and evaluative paragraph, the annotation. The purpose of the annotation is to inform the reader of the relevance, accuracy, and quality of the sources cited.
Annotations are different from abstracts. Abstracts are the purely descriptive summaries often found at the beginning of scholarly journal articles or in periodical indexes. Annotations are descriptive and critical; they expose the author's point of view, clarity and appropriateness of expression, and authority."
-handout from SOC 6010, by Cynthia Anderson, Associate Professor of Sociology, Fall 2019.
Your Style Guide (Chicago, APA, MLA) will most likely include a section on annotations, too.