Partition of British India, or
Continental Divide of the Americas
Or more generally, any major hydrological divide or topographical divide.
Hah! Wiki doesn't know everything! We need to 'leak' the knitting definition. The Great Divide is, as Deb Gemmell the queen of Top Down knitting says, the point in your knitting where you separate the sleeves from the body.
And that is exactly where I am in my two, top-down projects.
Featherweight, on the other hand still has a way to go.
There are 9 inches of body to be knit down from the sleeve separation point as well as 3/4 sleeves and major - three inch - edgings. I did try it on last night, after dividing for the sleeves and it seems to fit. That first trying-on of a top-down garment is a suspenseful event. Relief if it fits and there is no need to rip back and start over. Yet relief too, if it does need to be ripped back. How great to do it at this point in the knitting instead of when the sweater is complete. Such is the beauty of top-down knitting.
Once The Great Divide is passed, the knitting seems to go so much faster. There are, after all, only body OR sleeves stitches on the needle at once, not both. That makes The Great Divide, as Wiki says, major.