Directive words (also called task words) indicate what you have to do. Commonly used task words include describe, analyse or evaluate. The task word glossary lists and defines these words.
Limiting words make your task more specific. They include general constraints such as discuss one aspect, specify importance such as what is the main cause, or indicate specific time frames such as in the last two years, or in the 1980s.
Key words or key concepts are what are left when you remove the directive words and the limiting words from your topic. These will form the basis of your search strategy.
This process of helps to define your topic and begin to answer the question.