An abstract is a summary of a research paper that’s usually about a paragraph long. All research papers begin with an abstract to give a quick summary.
Sometimes, scientists haven’t finished up their research yet and want to present what they have at a conference. So they’ll write up a summary of what they’ve done and submit it so they can present it as a poster or an oral presentation at the conference. These abstracts sometimes get published in the corresponding journal for the conference (ie. the ASRM’s journal is Fertility and Sterility).
These abstract only publications are just snippets of the research that the author submitted. The researcher may go on to do more research and make a whole paper out of it, or the study may remain as an abstract only publication. Abstract only publications may not be peer reviewed and may contain errors.