The subject terms have been carefully selected to save you from having to look under many different words when researching a topic. For example, in Expanded Academic Index, all articles about cars are listed in the Subject Guide under automobiles. When you search in an index which offers subject searching check to see whether it has a thesaurus to help you. However no matter what an index calls its subject terms, the purpose for them remains the same - to help you search efficiently and effectively. A Thesaurus Can Help Your Search Many indexes have a thesaurus which defines the subject terms, suggests related and broader subject terms and gives the date when the subject term was first used in the database.
Definitions do vary from index to index.
For example searching about middle age in SocioFile for sociology articles and PsycInfo for psychology articles, you might be surprised that middle age does not cover the same age range in both indexes.