Why is cooking a food item method called different things by what the item is, or what is the criteria?

Well a quick one is poaching vs boiling because it’s actually based on the water temperature itself. Boiling happens when water reaches its boiling point of 212°F where liquid water bubbles heavily and is at its hottest point. You’d cook things like pasta in this. Poaching is at a substantially cooler temperature of around 120°-180°F where you have smaller bubbles for a much gentler cook. You’d use delicate foods like shell-less eggs or fish or potatoes you don’t want to overcook or break. In between that you have a simmer, which is usually used to render a dish without overcooking it.

Frying usually means you are coating something pretty heavily in oils/fats which can be done to the point of immersion via deep frying. Fried ingredients typically need to sit longer to get a crust. Sautéing is a dryer way of cooking with oil where you use just a little to coat the ingredients and hit them with consistent heat and movement. This keeps things like vegetables from burning while still getting a good texture and flavor from the heat.

All good but I'd just like to point something out.

When you boil pasta you're actually hydrating it, and it's a process that occurs above 80C, you don't need water to be boiling savagely.

In fact, it's preferable to let pasta simmer, as full boiling is a bit too "violent" and tends to damage most kinds of pasta.

You know, when some pieces are broken and torn like when it's overcooked? You can avoid that by keeping the temperature low.

Some people in Italy even turn the fire off after the water has started boiling ,as the water is hot enough to cook the pasta and keep it nice and firm.
- Interesting, I was taught you used a rolling boil for pasta so it wouldn't stick together. Maybe there's a halfway where it rolls for a few minutes then gets turned down as the pieces soften and become vulnerable to tearing.
The thing I've always found confusing is how American terminology as far as I can make out seems to almost always say "fry" to mean what I would always specify as "deep frying" and "sauteing" where I would usually say "fry". I think this is a Commonwealth countries thing and not just me. "Saute", to me had always seemed a kind of unusually fancy affectation for people working in restaurants with the average person eschewing it for the term "fry" until I started using YouTube and Google for recipes and got exposed to so much American material that I discovered they make these distinctions. I guess there's technical distinctions in how much oil you use in the pan (until the point of immersion where it's deep frying) but that seems much of a muchness.

Confusingly though I notice Americans seem to also sometimes use "fry" the way I would, but just sometimes. Eggs for example are "fried" but this is usually not meaning dropped in to a deep fryer. And then there's the confusion over the meaning of "grilling" vs "broiling" because as far as I can tell the term "broil" isn't used where I'm from and the the device Americans call a "broiler" is what we'd call a "grill" and things cooked under it are "grilled". I believe the American use of "grill" is referring to a shape of ridged cooking surface but then you get "grilled cheese" which I'd called "cheese on toast" or a "cheese toastie" which involves putting the sandwich in to a flat frying pan and which involves neither a broiler nor a ridged cooking surface and isn't referred to as sauteing nor frying. Then there's "griddled" which I think again is referring to a particular shape of cooking surface but given "grill" I just don't know.

Definitely some interesting variations within mostly shared vocabulary.
- Wow you definitely aren't american as I'm scratching my head to even figure out what you mean by some of these. The average grill in america is a standalone outdoor cooking station with a metal grate used as the cooking surface. They are also found in restaurants but usually they are in a bit of a different form that what the average American thinks of as a grill. the grates give the characteristic lines of grilled food that many seek. A griddle is a grill where the grate has been replaced by a flat piece of metal, often used for small or runny foods that would fall between the grates of a regular grill.
  
  We also dont typically have standalone broilers. Most american ovens have a broil option where the top heating element becomes very hot and can be used to brown the food.
  
  The main difference between grilling and broiling, in my american eyes, is how they are used. Grilling is a technique for cooking food from start to finish. Broiling is a technique used at the end of cooking something to brown it or something to that effect. I wouldn't use the broiler in my oven to cook a whole meal, and I wouldn't turn on the grill or griddle just to brown something.
  
  In my eyes saute is when you use only enough oil to keep something from sticking or burning, while frying is when you use enough oil that it starts to really add to the flavor of what you're cooking.
  
  I think the worst thing Americans have done is the air fryer though. Its just a fucking tiny convection oven, there's no frying going on at all. They just know us fat Americans are conditioned to salivate when we hear the word fry and cower in terror from big science words like 'convection' lol
- That's why I cook in French. Much clearer that way, and the recipes use proper units.
- G'day mate
You're correct but it begs the question, why the hell would they poach carrots? If any vegetable can stand up to boiling it's a carrot. Blanching I could see, (that's a 2 minute dunk in boiling water, OP, with a quick cooldown) if you wanted to pre-cook them so they wouldn't be harder than everything else. Maybe they were just being poncy.
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- Poaching in olive oil, butter, wine, etc would give a different flavor. I agree that water poached carrots would be just a slower way to cook carrots than boiling them.
Le sigh. Your answer makes me really wish we could have the equivalent of r/askculinary here.
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Looks like we were typing at the same time. I totally agree with everything here.
Wait you dont boil potatoes?
- I noticed that too, but I think they meant, "in the situation where you want the potatoes to come out a particular way".
  
  Their wording was "You’d use delicate foods like shell-less eggs or fish or potatoes you don’t want to overcook or break." Which could be a list of things that you don't boil including potatoes or a list of things that you don't boil and also potatoes in the special circumstance where you don't want those potatoes breaking.
  
  Honestly though I can't think of any circumstance where I've heard of potato being cooked by immersion in water where that water wasn't set to boil, they just take a long time to cook and need pretty heavy heat to soften so even when trying to be careful I'd find it strange not to boil them at all even if for just a shorter time frame.

Boiling and poaching are not the same. Frying and sautéing are not the same.

Why do you state this without making clear what the differences are? Useless comment ...
- I think it’s a pretty accurate answer. The OP asked why it’s sometimes calked poaching and sometimes boiling. The answer being that they aare different things.

Yes, there are differences between those things.

Poaching is cooking in hot liquid, but the liquid is not boiling or even simmering, so it is a lower temp than both.

Saute generally means you're using a small amount of oil/fat and stirring/tossing the food to spread the oil/fat around on everything while cooking everything. Pan frying generally means you're cooking a larger piece of something and not tossing it around.

So is Saute the same or similar thing like stir-frying?
- Similar, but I've only ever heard the term stir-fry used in combination with a wok over EXTREME heat.
- I think you saute at a lower heat than stir-frying

As pointed out already, these terms have quite specific and different meanings but it's worth being aware that they often get used interchangeably a lot too, and therefore possibly incorrectly. A lot of the specific terms will come from french cuisine (like saute) including all different names for exactly how you've sliced up your vegetables (julliene, brunoise etc). I believe this was so recipes could be written very precisely and therefore reproduced more acccurately.

It usually has to do with what chemical process happens to the food in question. Not all foods react the same to being dunked in boiling water. (Although I couldn't tell you what the difference between potatoes in boiling water and carrots in boiling water.) In the case of onions vs eggs, the same process is 1) extracting the water and using it to make sauce, with the onions, or 2) boiling off a tiny amount of liquid and heating the proteins to solidify them, in the case of eggs. Same method, wildly different chemistry.

Sometimes it has to do with how long that cooking method is applied, since a different thing happens. For example, you can poach OR hard-boil an egg; same method, different amount of cooking time.

In short, with a few exceptions, it's not about what process you're applying to cook the food, but about the result that it achieves in the food item.

Poached and hard boiled eggs vary by more than just their cook time. These names are much less about chemical processes and more about differences in technique. See other comments in this thread.
- If I hand you an egg and tell you it's a poached egg, you're going to thinking about the consistency of the egg, not how I cooked it. Poached means the result, not the process.

Poach equals lower temp liquid. It can be oil or water type liquid. Boil is maximum temp water type liquid only. Blanching is boiling for a short time with the intention of not cooking all of the way through (eg to get skin off or to prepare for preservation by freezing).

Fry and saute are used interchangably all the time. One person's fried onions is another's sauted onions. Saute should indicate small pieces turned or tossed in a moderate amout of fat. Fry can be small or large pieces and can have moderate to lots of fat as a cooking medium.

Note that this is how normal people in my region and life use these terms and I make no claim that this is 'right' just my experience.

It's not based on the item. You can boil turkey and poach eggs as well. Here's various definitions to get you started:

https://www.webstaurantstore.com/article/454/types-of-cooking-methods.html

I have no answers, just pointing out that boiled carrots and poached eggs are also things.

Boiling, poaching and blanching all have to do with how long something is immersed in boiling water, for instance. (I think, and those definitions may also subtly change with the food item.)

They're slight variations in technique. Poaching is usually at a lower temperature than boiling, for instance.

Boiling happens in boiling liquid, poaching happens at a lower temperature and you wouldnt boil turkey. Sauteing is frying but uses little fat, unlike deep frying for example.