"MeSH (Medical Subject Headings) is the NLM controlled vocabulary thesaurus used for indexing articles for PubMed"
from: Home - MeSH - NCBI [emphasis added].
Enter Mesh from the bottom of the default search screen. (Better yet, from the bookmark or favorite you make for MeSH in your browser.)
Unsure of how to identify MeSH terms? Use MeSH on Demand by copying and pasting text into the box. It will identify the MeSH terms in your text and provide related articles.
|Use AND for more specific results
niacin AND cholesterol
|Use OR to broaden a search with related terms
niacin OR vitamin B3
Image credit: "Logic Gates.svg" by HereToHelp, licensed under CC BY-SA 4.0, is available via Wikimedia Commons. Nancy R. Curtis cropped images from original graphic, and modified colors to accommodate color vision disabilities.