What keeps you up at night.
Tent, Definition One
A portable shelter of skins or cloths stretched over poles. Smaller, lighter tents use tanned rat hides, but that takes a lot of stitching and gets the rats mad. Larger and heavier tents use elephant hides, but again, those are hard to come by. (Problems related to acquisition include poking by tusk, trampling by stompy-feet, and criminal trial in international court, among other things.)
Tent, Definition Two
A synonym for tent is collapsible shelter, which, sadly, is true.
Tent, Definition Three
The main idea in the concept of tent is stretch. As in it being a long stretch to make something as improbable as a tent actually usable.
Then, once you have the concept down, you have to figure out how to make it happen. You can't make a tent out of just anything (rat pelts excepted). No.
Tents (the coverings of tents anyway) are tricky. They have to accept stress and thrive on it, no matter what direction it comes from, and tents have to be agreeable to being taken down, wadded up, and stuffed somewhere, sometimes for a long while, in the dark, with no air at all to speak of, until they are taken out again and stretched.
Tent fabrics must be light enough to carry yet impervious to wind and rain. This is so hard to do that most tents made for backpacking have two shells. These are called double walled tents, but that's only to make you feel safe.
No tent is like a wall in any way, but you get the feeling of security and safety with the idea of having two of something, so that's partly why it's done. The outer covering is waterproof and also impervious to bird poo, which is a pretty good thing as far as it goes.
Yes, these are great benefits in themselves, but there's more.
The inner covering (inner wall) is not waterproof, but mostly, though not completely, windproof, in a lot of tents. This means that you can have quite a bit of protection inside the two shells, both from wind and rain, without getting all wet from condensation (assuming that you do any heavy breathing at all), and also without suffocating.
The downside of not suffocating, of course, is that you have to get up the next day and do more backpacking, but some people (this is actually true) prefer hiking to dying peacefully in bed which requires no effort at all, and is also free from biting flies.
Well, back to the story...
The part of the tent that is not the walls is not especially important. It is a frame of some kind, though you can rig up a tent with no frame but using ropes pulling from the outside to the same effect. Or you can use mammoth ribs, sticks, or fiberglass hoops on the inside (or the outside, if you're a hinky bastard). They all work, these frames and ropes, but without the covering there isn't much point in having the frame.
OK, this is a stretch of another kind, but in case, just in case you do have a tent made of elephant hides, and the relatives of those elephants hear that you're in the neighborhood, they may stop by to mete out a little informal, wrath-based justice, so if you have a frame of some kind, like sticks or poles, you can at least poke back at them if they get all tusky on you, before they give up on the preliminaries and just do the stomping thing.
Well, truth be told, even if it is feeble, the poking back will give you something to do in those last few seconds of life, if you have a really short attention span and would get bored otherwise.
But. If your tent is made of rat hides – wo. Once the rats start their angry swarming all you hear (if anything at all) is a rustling, rushing sound about a half second before there's nothing left of you but a few scattered gnawed bones. So don't worry about boredom there – you're covered. In rats.
Until that happens you'll be dry and snug and feeling safe inside your tent with its imaginary sense of security.
Tent, The Postscript
But then the whole idea of tents is kind of sissy, since real men (in the olden days at least) were supposed to simply roll up in a blanket at night and shiver like crazy for hours and hours, which is why they got up a lot earlier back then, to make the shivering stop. And since you already had the horse, it wouldn't have been that big a deal to carry the required wooden poles and steel stakes and rope and the whole waxed canvas tent itself, but someone might call you a sissy for it. But if someone did call you a sissy for it, you just plugged them and got on with it.
Backpacking is different now. We walk a lot more, whine about horses instead of riding them, and the wax is only on our dental floss, which no one but heavy-weight backpackers carries any more. And no guns. We don't even get to carry guns and shoot these days. Unless we're in a national park, where guns are now legal. Heh.