MEDLINE is a database created by the National Library of Medicine. It contains full text articles from over 1,400 biomedical journals dating back to 1936. Disciplines covered include medicine, nursing, dentistry, veterinary medicine, health care, and pre-clinical sciences.
MESH stands for Medical Subject Headings. It is the National Library of Medicine's controlled vocabulary, or list of standardized terms, which are used to describe the content of an article. There are over 26,000 MESH terms arranged in a hierarchy, or tree structure. This hierarchy allows for browsing broader, narrower, or related terms.
For example in this view of MESH, Infection Control is a broad term and Antisepsis and Sterilization are narrower, or more precise, terms.
In MEDLINE an abbreviated list of subject headings show on the search results screen.
Watch this detailed tutorial Using the CINAHL/MeSH Headings Feature. Standard YouTube License (time 3:32) https://youtu.be/eJJPp9yAIoA