What's a Gruzzle?

So, what's a Gruzzle?  With extensive use of Venn Diagrams, GL Hoffman often posts these visual blog posts on his blog, What Would Dad Say, and Fast Company has also started pubishing them as well.

So back to the original question, What's a Gruzzle?  Here's a really good answer, by one of his readers:

But here's the official answer:

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