MEDLINE is one of the most important information sources in medicine and related life sciences. Database MEDLINE is available in OVID interface, covers the international literature on biomedicine, including the allied health fields and the biological and physical sciences, humanities, and information science as they relate to medicine and health care. It contains bibliographical records and abstracts, information is indexed from approximately 5,600 journals published world-wide.

The National Library of Medicine (database producer) uses the Medical Subject Headings (MeSH) thesaurus for the document-centered indexing of documents.

You can also use the Term Finder in Advanced Search, thanks to which you can search for suitable terms for search queries in one place using several subject heading dictionaries, including the MeSH thesaurus. See this page for details.
A short video with a demonstration of practical use can be viewed at https://www.brainshark.com/wkovid/vu?pi=zHAzerbGjz34XJz0.