This applies only to North America I need to emphasize, and really most of this information isn’t terribly relevant to home bakers, but you know I like to be thorough. So here goes.
You’ll perhaps remember from the below post the “fairly coarse, fairly dark” flour you get when you grind the whole endosperm of a wheat berry with the bran and germ removed? Well that’s what we in the States call “straight” flour. We generally don’t bake with it, we sift it, though the French frequently use it for bread flour. Just another reason why replicating French breads in the US is difficult.
But I digress. Straight flour, as I mentioned below, is sifted into different grades before it’s sold. Remember all those levels of sifting I discussed? Well any flour that’s made from those siftings — minus the “shorts”, the pieces of tough outer endosperm — is called a “patent” flour. Patent flours encompass all the flours commonly sold in stores including bread flours, all-purpose flours and pastry and cake flours. As such, patent flours can have highly variable extraction rates. “Extra short” patent flours have the lowest extraction rates (i.e. are cake and pastry flours) and “medium” or “long” patent flours have the highest and are used for bread.
“Clear flour” is what’s left when all the higher quality patent-grade endosperm has fallen through the sifters. It’s not “clear” at all but rather extremely dark, being the tough bran and germ-tinged endosperm that literally cleared the sifters without falling through. It’s normally used by professional artisan bakers to make rye or peasant-style breads, though these days it is possible to find clear flour online…for hard core country bread lovers only. Clear flour also comes in three grades: fancy (the lightest), first and second.
The very lowest grade of flour is sometimes called “red dog” flour and is typically sold as livestock feed or to make pet food.