Known as Boolean operators - AND, OR and NOT are used to combine search terms.
These operators can be used to combine MeSH terms or keywords within a line of your search or to combine different lines. This is how you combine the separate concepts of your search.
For example, in this search the hand hygiene and hand disinfection terms are combined together,
then the results compared against guideline adherence.
Nesting can be used to keep search items together to suit your search. These will give different results
A and B or C
(A and B) or C
A and (B or C)
All these methods can be combined.
Note that PubMed does not allow proximity searching.
In some databases the syntax may differ slightly - check the Help section for correct terminology.