Keywords are exactly that: a series of key words that help a researcher discover what information can be found in a particular article or book. In academic library research, the keywords will help you construct a comprehensive search in a journal or database to help you find material that might be useful to you. Keyword searching is a broad form of searching that will enable you to discover if a specific term has been used in an article, an abstract, or somewhere else on the page.
Unlike subject headings, which are made up of "controlled language" used by catalogers, keywords represent natural language used in everyday life. For example, you may be researching "chronic disease" and prevention. One of the formal subject headings in the database CINAHL for finding information on this topic is "chronic disease prevention and control." Most researchers wouldn't think to search using that term. But if you do use the subject term paired with cancer you retrieve 42 results whereas if you search "chronic disease" and prevention and control and cancer you will retrieve 92 items. Using subject headings can be helpful in focusing your search to the most relevant results; and using subject headings and keywords together is a common research practice.
Knowing the right keywords to search will help you start your search off right. Often, when you aren't finding good information - or any information at all about a topic - it is because you haven't yet figured out the correct keywords.
The best thing you can do before ever getting into a database is to think about the keywords that will best represent your topic. Write down your thesis statement and pull out the major terms in it. Then, think of as many different ways as you can to say those key terms. For example if you were researching:
Chronic disease among minority populations in urban areas.
Some keywords in this sentence are: "chronic disease", minority, and urban. However, searching for these terms will get you only a fraction of the material that is out there, because if a different keyword is used to express the same concept you need to search for that keyword as well. So, other keywords that would be useful to use when researching this thesis topic would be heart disease, stroke, cancer, diabetes, obesity, and arthritis (to represent chronic diseases); Asian American, Black, African American, Hispanic, Latino, Native Hawaiian, Other Pacific Islander, American Indian, Alaska Native (to represent minority populations); and other words to represent urban such as inner-city, metropolitan area, and city. You could also refine your search, and your thesis, by narrowing to a specific sub-set of a population (e.g., adolescents).
Setting a list of terms and then combining them in the databases will yeild you the best results.
Remember that you can combine keywords using the search limiters AND, OR, NOT. These will narrow or expand your search.
Use quotation marks around words that make a phrase. Search for "health promotion" rather than health promotion or health AND promotion in a database. This will ensure that the database knows that you want the phrase "health promotion" and not every article with the word health and the word promotion in it! The same can be said about "chronic disease".
Tailor your keywords to the database. Not all databases will pick up all keywords. Get your list of keywords and plug them into various databases to see whether or not they are useful for you in that database. If you go into a database with keywords and don't find anything, don't get discouraged. Take your words to a different database and see what you find there.