Main headings (also called "MeSH headings," "preferred terms," or "descriptors") represent concepts found in the biomedical literature. These records are topical headings that are used to index citations in MEDLINE, for cataloging of publications, and for use in other databases. Most main headings indicate the subject of an indexed item. For a journal article, main headings describe what the article is about. Main headings are generally added or revised in the MeSH vocabulary on an annual basis.

Looking at our PubMed record example (https://pubmed.ncbi.nlm.nih.gov/17612905/ ), you can see the main headings listed on the left under MeSH terms. These are the capitalized terms, to the left of the slash ( / ). These include terms such as Blood Pressure, Double-Blind Method, Humans, and Hypertension.