Keywords are simply the terms that you use to search for a topic. They're the main words of your topic.  They're sometimes called the essential terms.

OK, let's pretend your topic is pet therapy for elderly patients suffering from depression.

Your keywords would be pet therapy, elderly patients, depression.  Those are the terms you would type into a library database to start finding sources.

When thinking of keywords, try to think of alternate terms in case your first set of keywords does not find enough information on your topic.  Think of synonyms, broader terms, narrower terms, and related terms using a matrix like this:

After we've brainstormed keywords to search for our topics, we'll next want to connect our keywords with one of these operators when we type our search into the library's search engine: AND, OR, NOT, "", *

Connecting keywords with AND, OR, NOT "" is called Boolean Searching.  Most library search tools use Boolean searching. 

When you type your search into the library search tools, try to use one of the Boolean operators.  Please capitalize the operators AND, OR, NOT.     

Please watch the guest video below Pirates vs. Ninjas (3 minutes) from Pollack Library to learn how AND, OR, NOT works in a search