Defination, Analogy, Examples and Explanation

There are four surprises when I ask children to explain me a concept. For example, 'Green House Effect'.

1. Some children give me definition of Green House Effect (courtesy text-book). A definition is basically most precise explanation of the concept in least amount of words. But a correct definition doesn't tell me if the child has understood the concept.
2. Some children give me analogy of the concept. But analogies fail when applied outside their narrow domain. So this still doesn't tell me if the child has got correct (i.e. necessary and sufficient) understanding of the concept.
   
3. A few children will give me Examples of the concept - which is application of the concepts to specific situation. But examples is not the same as explanation.
4. Then there are a few who can explain the concept in ways that even I may not have thought-of. If I start shooting holes in their explanation typically - they can 'separate wheat from chaff'.
   

How should one convey the difference between definition, analogy, example and explanation.