Keywords are the main concepts of your research topic and/or question.
When you are searching for books and articles on your topic, you will need to select some keywords. Keywords help point your search in the right direction and are like the main ideas in a sentence or paragraph. The words in your research question are perfect starting points.
For example, What are the causes of global warming? The keywords are causes and global warming. But there are other words that might help you.
Terms that mean the same thing (synonyms) are also worthwhile keywords.
Global warming is sometimes called climate change and drug use among athletes is sometimes called doping. Using different terms to locate information will give you greater results.