Q. What are Boolean operators? How do they work?

AND

Finds only records containing all of the specified words or phrases. Septic AND shock finds records with both the word "septic" and the word "shock"

OR

Finds records containing at least one of the specified words or phrases. septic OR shock finds records containing either septic or shock. The found records could contain both, but do not have to.

NOT

Excludes records containing the specified word or phrase. septic NOT shock finds records with septic but not containing shock.

These operators work in many different resources, like PubMed or Google.