Defining 'The'

[Daij]

Hi
I am compiling a number of language based 'teasers'. I have a good one here and very few people give good answers. I wonder if anyone would like a try;

"Imagine that I am from Mars. I have told you that I speak perfect English apart from one thing. I do not understand what this word means – ‘The’.
Can you explain to me what this word means, but bear in mind that you cannot use this word in your definition? If you do, I won’t understand your definition."

If my compilation reads well, I may try to get it published. If I am successful, if you object to your definition appearing, please indicate with your reply