The Use term has been chosen by the indexers as the preferred term. Generally, you'll want to search the Use term instead of the Used For term, especially if you are searching the Key Terms field. See Used For . Generally, search the Use term instead. You may want to search both terms, however, if you are searching the Basic Search field.
Language is broader than English , or Spanish , for example.
Terms with similar meanings are Synonyms, e.g., dog and canine. Generally, search the active term instead of the Synonym. You may want to search both terms if you are searching the Basic Field, however. Since Basic Search includes fields other than Key Terms, such as Title and Abstract, the key term indexing may be too limiting. An Abbreviation for the base term has been used in the database.