Define is another of the more straightforward of the key terms. Typically, a teacher asking you to define a term is asking for a translation of a technical term into language anyone could understand. Defining a concept calls for more elaboration, but it still builds on strategies for definition.
Writing tip: Standard definitions use a variety of strategies including synonyms, antonyms, analogies, comparisons, and explanations of where a term came from or the contexts in which it is used. If you've studied dictionary definitions for the terms, you can also build on those. Teachers are usually interested in seeing that you understand key terms, though, so when they ask you to define a term they sometimes also want you to show that you can apply it to a particular context. You can get a better sense of how long and detailed you should make the definitions based on the points allotted to the definitions and the number of words/concepts you're expected to define.