Preprint

A preprint is a complete draft of a research paper posted publicly, usually on a preprint server, before or during peer review. Preprints speed up the circulation of findings and are free to read, but their claims have not yet been vetted by independent reviewers. Many preprints are later published in revised form; some change substantially, and some are never published at all.

In fast-moving fields, ignoring preprints means missing the newest work relevant to your thesis, so they are often worth reading. Cite them cautiously: label them as preprints, check whether a peer-reviewed version now exists and cite that instead, and give less evidentiary weight to unreviewed claims, especially ones central to your argument. Your examiners will expect you to know which of your key sources have and have not passed review.