What is Freewriting?

From Mark Levy's website. He's the author of Accidental Genius: Using Writing to Generate Your Best Ideas, Insight and Content. 

"Freewriting is deceptively simple: Start writing as fast as you can, for as long as you can, about a subject you care deeply about, while ignoring the standard rules of grammar and spelling. Your internal editor won’t be able to keep up with your output, and will be temporarily shunted into the background. You’ll now be able to think more honestly and resourcefully than before, and will generate breakthrough ideas and solutions that you couldn’t have created any other way."