What are MeSH terms and why do I have to search with them?
Answer
In Medline and PubMed (the public and free version of Medline), the controlled vocabulary/subject headings are called MeSH which stands for "Medical Subject Headings". These are assigned topics to articles that capture the essence and the main ideas of the article. It is important to search for subject headings for numerous reasons because it helps capture articles that have been assigned with the same subject heading that we might not have otherwise captured with keyword searching, as sometimes we can't think of all the possible synonyms related to a topic. They're also important to search for because sometimes articles are poorly indexed in Medline, meaning there might not be an abstract that we can search in, or a meaningful title.
See also "What are controlled vocabularies" and "Why do I have to search for subject headings AND keywords?" for more information.