MeSH is a great resource,a thesaurus, especially significant if you access Medline – from whatever source. (PubMed is the free version, accessible everywhere anyone has access to the internet.)
MeSH means Medical Subject Headings. They are assigned by indexers at the National Library of Medicine. This thesaurus is complete with definitions or scope notes. It is organized in a hierarchical fashion so that if you wanted to search all antibiotics, for example, you wouldn’t have to separately type all of them, but could just “explode” the main heading. You can limit the headings to a major concept, the most important concept(s) in the article. You can also attach subheadings, such as adverse effects of antibiotics.
Every year the indexers at the National Library of Medicine update the Medical Subject Headings (MeSH) based on the latest usage of biomedical, pharmaceutical, public health and disease terminology.
*NLM Technical Bulletin, Nov-Dec 2009, Newly Maintained MEDLINE for 2010 MeSH Now Available in PubMed