Keywords, also called search terms, are the words you enter into the search boxes in catalogs, databases, and search engines. They represent the main concepts of your research topic.
Descriptors, or subject headings, are terms used by the creators of a database to "officially" label a particular concept. This is referred to as a controlled vocabulary.
It is generally easier to start your search by using keywords, but if the resource you are searching supplies you with descriptors, you may want to incorporate those into your search for more relevant results.
Before you start searching, take a moment to consider what keywords you will use.
Be prepared to run multiple searches using various keywords. It's rare that your first search will bring back perfect results.
Here is an example of a research question: What is the impact of college binge-drinking on school performance?
Identify the key concepts: college, binge-drinking, school performance
Identify synonyms or related terms
Because the databases search for the exact words you enter, certain types of words can be unhelpful to include in your search. These include:
relationship words -- those that get at the relationship between two topics. Examples: compare, contrast, correlation, causation, relationship
judgement words -- those that judge something to be better or worse than something else. Examples; best, worst, pro, con, advantages, disadvantages
It may be that you will have success using these terms, but since there are many ways these ideas can be express or implied, using these terms in your searches may exclude relevant articles simply because they don't include the exact word that you entered.
Usually you'll want to spell out abbreviations when searching databases and search engines. But you can also search for both the abbreviation and the complete word or phraseby connecting the terms with OR.
Example: Cognitive Behavior Therapy OR CBT
As explained above, descriptors are standardized language used by a database to describe concepts. You can usually find the database's controlled vocabulary in a section called subject terms or thesaurus. Be aware that each database can have their own controlled vocabulary, so the language used to describe a concept may not be consistent across databases.
From: Cooper, Harris, Harris M Cooper, and Larry V. Hedges. 1994. The Handbook of research synthesis. New York: Russell Sage Foundation.