PhD and EdD in Kinesiology

Boolean operators define the relationship between search terms.

• AND searches for all of the search terms. The AND operator limits the search because the sources in the results must contain both terms.
• OR searches for either of the search terms. The OR operator expands the search because the sources in the results can contain either term.
• NOT excludes the search term immediately after the NOT operator. The NOT operator limits the search because the sources in the results cannot include the term following the word NOT.

Example:
diabetes AND children = articles about children with diabetes
diabetes OR children = articles about either diabetes or children 
diabetes NOT children = articles about diabetes, but excludes articles mentioning children with diabetes

Here is a series of Venn diagrams to show you how the Boolean operators limit or expand searches.

Image attribution: CC BY-SA 4.0 by Cecelia Vetter

MeSH (Medical Subject Headings), the National Library of Medicine's controlled vocabulary thesaurus, consists of terms naming descriptors in a hierarchical structure that permits searching at various levels of specificity.

In other words, MeSH terms describe what an article is about and are used to label all articles on a topic even if different authors use different words for the same concept (such as cancer vs. neoplasm vs. tumor).