Boolean Operators or Boolean Connectors

George Boole was an English mathematician who helped establish the modern field of mathematics called symbolic logic. Boolean logic uses words called operators. The three main operators are: AND, OR and NOT.

Databases use Boolean logic to locate only those items that match your search.
George Boole
1815 - 1864
  
The blue areas in the following diagrams represent the number of hits you would receive from doing a search using the Boolean operators AND or OR in the same database:

using AND narrows the number of items returned:
using OR retrieves a large number of items:
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