A bibliography is a list of sources (books, journals, websites, periodicals, etc.) one has used for researching a topic. Bibliographies are sometimes called "references" or "works cited" depending on the style format you are using. A bibliography usually just includes the bibliographic information (i.e., the author, title, publisher, etc.).
An annotation is a summary and/or evaluation.
Therefore, an annotated bibliography includes a summary and/or evaluation of each of the sources. Depending on your project or the assignment, your annotations may include one or more of the following types of writing:
Your annotated bibliography may include some of these, all of these, or even others. If you're doing this for a class, you should get specific guidelines from your instructor.
Information taken from the Annotated Bibliographies created by the OWL Purdue Online Writing Lab.
Abstracts are descriptive summaries that present the main points or focus of specific works (e.g., articles, books, conference proceedings). They normally do not include a critique or evaluation of the work. Abstracts usually appear at the beginning of scholarly journal articles and in the library databases (e.g., article search results list and database article records). An abstract's purpose is to help you decide whether an article is relevant to your research.
Annotations also cover specific works (e.g., articles, books, conference proceedings) but they can include descriptive summaries, evaluative summaries, or a combination of both. A descriptive annotation summarizes the scope and content of a work whereas an evaluative annotation provides critical comment. Annotations usually appear in an annotated bibliography. Many instructors will include both an annotated bibliography as well as a research paper as part of a course's required assignments. You will typically complete an annotated bibliography assignment before you begin work on a research paper. Completing an annotated bibliography first will help you organize and write your research paper.
Image taken from Bibliography.com, MLA Annotated Bibliography Examples and Writing Guide, By Jennifer Betts, https://www.bibliography.com/mla/how-to-write-a-annotated-bibliography-in-mla-style/