Preprint
"...a complete and public draft of a scientific document. Preprints are typically unreviewed manuscripts written in the style of a peer-reviewed journal article. Scientists issue preprints to speed dissemination, establish priority, obtain feedback, and offset publication bias."
https://grants.nih.gov/grants/guide/notice-files/not-od-17-050.html
Postprint
An author’s final manuscript, which has been peer-reviewed (if applicable to the publisher's policies). It has not, however, been copyedited nor does it reflect any layout by the publisher in preparation for publication.
Preregistered Protocol
"where a scientist publicly declares key elements of their research protocol in advance. Preregistration can help scientists enhance the rigor of their work."
https://grants.nih.gov/grants/guide/notice-files/not-od-17-050.html
Preprints and postprints (also called the author's final manuscript or author's accepted manuscript) can be posted in repositories (i.e., RED, PubMed Central). Often, researchers can share and/or retain the rights to these versions of their manuscript.
Sherpa Romeo can assist researchers in understanding their rights for archiving these versions of their manuscript and understanding publishers' policies.