Winter Onions go by several different names: Egyptian Walking Onions, Tree Onions, and Top Onions. Each of these names describes a different characteristic of the plant.
Homesteaders of days gone by kept a patch of these onions in their garden year round. Even Thomas Jefferson had them growing in his garden at Monticello! They are a perennial plant that can take extremely cold temperatures, so our ancestors grew these onions along with their other permanent vegetables like rhubarb and asparagus. They always survived the winter, that's why they're called "Winter Onions".
The other names refer to how the onions actually grow. The plant forms a small bulb below ground and a cluster of baby bulbs on top of their tall, hollow stalks. Hence the name "Top Onion". The tiny bulbs begin to sprout, and the resulting mass resembles miniature tree branches--that's where the "Tree Onion" name comes in. Eventually these clusters become too heavy for the stalk to bear, so the stalk tips over, the bulbs touch the ground, and they begin to take root. This helps the plant spread, or "walk". The "Egyptian" part of the name most likely refers to the fascination the Egyptians had with onions, but no one knows for sure. It certainly makes the plant sound more exotic!
Every part of this onion plant is edible. That feature made it incredibly valuable to the old-timers, who couldn't run to Wal-Mart every time their cupboard got a bit low. The root bulb, though smaller than the onions we buy at the supermarket, can be used just like any other onion. The stalks can be chopped and used like chives, and they're milder than the onion bulb itself. The baby bulbs are very flavorful and are great in soups and stews, and some folks even pickle them!
A few years back I mentioned finding these onions to my granny and I asked her if she knew about them. She said, "Why, yes. I've been growing those onions since I was a kid. Go on out back and dig you up a few of mine and add them to your patch. I hate to see them die off when I'm gone." So I did. And now those very onions that have been in my family for a hundred years have started to walk right out of their spot in my garden. I can take the hint, so this spring I'll be out there digging my onions and passing them around to anybody in my family who wants to grow a little part of Granny's garden. Sadly, we don't have her with us anymore, but by golly, we can sure honor her wishes by keeping her onion patch alive!