MeSH stands for Medical Subject Headings, the list of standard terms added by indexers to PubMed article records to help improve search results. National Library of Medicine indexers examine articles and assign the most specific MeSH headings that describe the concepts discussed. MeSH terms help assure that search results will include the articles about a topic, even when different words are used to describe the topic in the title and abstract.
PubMed works "behind the scenes" to match your search words to the related MeSH term. The actual search used is displayed in the Search Details box on the right hand side of the screen. Here is the Search Details box for a search entered as Yoga AND Anxiety.
When you find an article of interest, look at the MeSH terms assigned by the to help you find additional words to use to focus your search. Click on the title of the article and then click on the Publication Types, MeSH Terms link under the abstract.
To the left are the MeSH terms assigned to the article The effects of yoga on anxiety and stress. After looking at the list you may realize that adding the words Treatment Outcome to the search will help focus it on articles that measure the outcome of an intervention.
Articles labeled PubMed -- In process will not yet have a list of terms.
The MeSH Database provides you with a way to search for a MeSH term and find how it is used. For example, when you enter a search for Drug Abuse in the PubMed search box the Search Details shows that the MeSH Term Substance-Related Disorders was searched. You notice that your results include articles about alcoholism and tobacco abuse that you would like to exclude.
Use the drop-down list next to the search box to search the term in the MeSH Database.
The link to Substance Related Disorders on the results list tells you how the term is used in the database. Since this definition is broader than your intent, click on the Substance Related Disorders link and scroll down on the next page to look for more specific terms. All of the narrower terms in the list are searched when Substance-Related Disorders is searched.
Use just the more specific drug terms like Amphetamine-Related Disorders OR Cocaine-Related Disorders to eliminate alcohol and tobacco (further down the list) from the results.