On writing a million words

They say you don't get good at writing until you've written a million words. I'm not really sure what that means. Does it mean you need to write a million words of fiction in order to be a good fiction writer, or is that million words any words that you've written? If it's any words you've written in your lifetime, then I'm pretty sure I've eclipsed the million word mark. If it's a million words of fiction writing, such as novels, short stories etc., I'm probably well below that level.

I kind of like the 10,000 hour approach. Basically that is that one must spend a minimum of 10,000 hours at something in order to become really good at it. It's definitely a good rule of thumb for guitar practice, and I'm pretty sure I could become a darn good writer if I spent 10k hours doing it. I don't know about golfing though. I'd probably become better, but that would just get my hopes up and get me spending more money playing golf, which, since I've only golfed twice in my life, would be a substantial increase. Still if 10,000 hours would make me really good at it, perhaps I could make it back.

Back to writing, I've started a "million word" file in OpenOffice and I'm trying go do as many words as possible. Still though, it would help to know if they all need to be fiction in order for me to become great at writing fiction.