If you can't explain it to a 6-year old...
Definitions are the mind's comfort food. Why bother going on a rigorous diet of learning in detail how things work when you can pluck a definition out of a dictionary and ride with it?
It's a rhetorical question, definitions never solve the immense task of explaining the world and its various bits to a 6-year old.
Unless the knowledge has been ingurgitated and digested properly, until it's become part of oneself, there is no way any child would accept a packaged explanation.
Is that why the best sites on astronomical topics are those made for kids?