Here's a breakdown:
* Most journal articles require an abstract: This is because journals need a concise summary for indexing and searching.
* Student papers often require an abstract: Instructors may require it to help students develop concise writing skills and to provide a clear overview of their work.
* Other types of papers may not need an abstract: This includes reports, essays, and other types of papers that are not intended for publication.
To be sure whether an abstract is required, check the specific instructions for your paper.
If you're writing for a journal, refer to their submission guidelines. If you're writing for a class, ask your instructor.