(1) What keeps you up at night because of all the flapping.
(2) 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 tends to annoy the rats. 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.)
(3) A synonym for tent is "collapsible shelter", which is, sadly, all too often true.
(4) In the abstract...
The main idea in the concept of tent is stretch. As in being a long stretch to make something as improbable as a tent actually usable.
But then, once you have the concept down, you have to figure out how to make it happen. You can't build 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. Again.
Tent fabrics must be light enough to carry, yet impervious to wind and rain. This is so hard to get right that most tents made for backpacking have to be made twice, with twice the normal number walls. They have these two shells, and their own moniker. They are called "double walled tents", but really that's only to make you feel safe. No tent is like a wall in any way whatsoever, but you get the feeling of security and safety with the idea of having two of something instead of just one, which is what you get with a "single walled tent", so that's partly why it's done.
The outer covering of a double walled tent is waterproof and also impervious to bird poo, which is a pretty good thing. Yes, these are great benefits in themselves, but there is more. The inner covering (inner wall) is not waterproof, but mostly, kinda, though not completely, windproof, in a lot of tents. And breathable. This inner covering is pretty breathable, and can be, because the bird poop never gets to it.
This means that you can have quite a bit of protection inside your two shells, from both wind and rain, without getting all wet from condensation either (assuming that you keep the heavy breathing episodes down around normal levels), 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 in fact true) prefer hiking to dying peacefully in bed, which requires no effort at all, and is also free from additional complications like biting flies, mosquitoes, and stinky companions.
Well, back to the story...
The part of the tent that is not the walls is also not especially interesting. It is a frame of some kind, though you can rig up a tent with no frame by using ropes pulling from the outside to the same effect, or jury rig a frame from sticks that you might find lying around, if you are exceptionally smart, and good with your hands, and have lots of time, and like to swear while you work.
Or you can use mammoth ribs 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. Unless...
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, fury-fueled justice, so if you have a frame of some kind, like sticks or poles, you at least have something to poke back with if they get all tusky on you, before they give up on the preliminaries and just get right down to the stomping.
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 built-in imaginary sense of smug security.
(5) Postscript, eh?
But you know, the whole idea of tents is kind of sissy, since real men (in the olden days at least, when all men were tough, and cowboys) were supposed to simply roll up in a blanket at night and shiver like crazy for hours and hours while pretending to sleep, which is why they got up a lot earlier back then. To make the shivering stop.
And since you already had the horse (a required accessory for all cowboys), 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 doing that. But if someone did call you a sissy for it, you would plug them with a few rounds from your Colt and got back to business, so it was probably a wash.
Backpacking is different. Backpackers walk a lot more, whine about horses instead of riding them, and the only wax is 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 up the landscape these days. Unless we're in a national park, where it's now legal to carry them. (United States only, I hear.)
Heh.