There are 3 Magic Words, called Boolean terms (sometimes called Boolean operators, or command terms), you can use to connect or disconnect keywords.
Think of them like interlocking bricks, like Lego. Each brick stands alone, but you can also snap them together to create one larger piece. You can snap a brick off to shorten your piece.
When you apply this "Lego concept" to keyword searching, you tell the search tool (database) to look for multiple terms/concepts at once, which will make your search more precise -- or you may allow the database to search for alternative terms that will bring back more results.
Using the 3 Magic Words singly or in combination creates a more precise and powerful search, with a higher percentage of relevant results.
AND connects different concepts. AND limits your search and reduces results by making them more precise.
Jack AND Jill: results about both Jack AND Jill; ignores results that don’t mention both
The more keywords you connect with AND, the fewer results you will retrieve. The database will need to find each of your keywords in the text in order to show it to you.
OR combines concepts.
OR expands your search and increases results. This can retrieve an overwhelming large number of search results!
Jack OR Jill: results about either Jack OR Jill
Using OR is helpful when we are searching for a concept that is described equally well by more than one term.
NOT excludes concepts and reduces results.
Use with caution! It can remove relevant results.
Jill NOT Jack: results about Jill but without any mention of Jack
This type of search is good to use when you already know what you do NOT want.