An abstract is a self-contained, short, and powerful statement that describes a larger work.
An abstract of a social science or scientific work may contain the scope, purpose, results, and contents of the work.
An abstract of a humanities work may contain the thesis, background, and conclusion of the larger work.
The abstract is not a review, nor does it evaluate the work being abstracted. While it contains key words found in the larger work
The abstract is an original document rather than an excerpted passage.