ERIC.ED.GOV website information:
Boolean Operators
AND
Use AND to narrow a search and retrieve records containing all of the words it separates, e.g. adolescents AND children will only find records containing both these words.
OR
Use OR to broaden a search and retrieve records containing any of the words it separates, e.g.adolescents OR children will find records containing adolescents only, children only, or both words.
NOT
Use NOT to narrow a search and retrieve records that do not contain the term following it, e.g. adolescents NOT children will find records that contain adolescents, but will not contain the word children.