An explanation or answer to a question that sounds logical at first but after thinking about it, is clearly flawed or outright wrong.
A good application of this concept is when making "lurple" answers to multiple choice questions. You want answers that sound like they might be correct but in fact, are wrong.
Another example of a lurple is when a someone tries to explain Intelligent Design rationally. Or their explanation as to why the Earth is only 6000 years old. The only way to succeed is to bypass the intellect with lurples.
The word originated in McLean, VA by a local High School Freshman in early 2009. (He was trying to come up with a word that rimed with purple.)