George Boole was a 19th century mathematician and philosopher (1815-1864). He invented what we refer to as Boolean logic, a method of combining factors to limit or increase results. Boolean logic utilizes the operators AND, OR, and NOT to describe what will or will not be included in search results.
e.g. Strawberry OR Vanilla OR Chocolate
Strawberry AND Vanilla AND Chocolate
Strawberry OR Vanilla NOT Chocolate
When you are searching for a concept that may be described using several synonymous terms (e.g. car, automobile, vehicle) you want to increase your recall by linking these synonyms using OR. When you search for car OR automobile OR vehicle the search engine will retrieve results that include at least one of these terms.
Takeaway point: The OR term brings back anything and everything. It is best used for searching for synonyms (cats OR felines) in order to increase recall.
If you were looking for something very specific, say an article or book that includes all of the terms car, automobile, and vehicle, you would want to increase relevance by using the AND operator. Doing this will bring you only results that include all three terms.
Takeaway: The AND term is limits your search, and is best used for combining different concepts (presidents AND statues) and for refining results (cats AND breeds).
If you want to be the most specific and you are looking for results that include one particular term and don't include variations, you can use the NOT operator. So if you are looking for results that include only the term car but not the terms automobile or vehicle you would search for car NOT automobile NOT vehicle. This will exclude any items that include those two terms from your results.
Takeaway: The NOT operator is best used to exclude
confounding terms or concepts (e.g. nursing
NOT motherhood), eliminate specific subtopics (horsemanship NOT bridling), or fine-tune broad topics (cats NOT wild).