Nesting (or ' GROUPING') is a keyword search technique that keeps alike concepts together, and tells a search engine or database to search those terms placed in parentheses first.
Use parentheses to group similar concepts when you need to use two or more connectors.
For example, the search:
alcohol AND (adolescents OR teenagers)
will retrieve records having the terms ALCOHOL and ADOLESCENTS, as well as items with ALCOHOL and TEENAGERS.