Most culinary terms are French. A few are Italian, some are even English, and others are determined by specific ethnic cuisine. Once you've learned to cook, you throw them around as though everyone knows what they mean. You may use them yourself without really knowing what you're talking about. Then, there's the menu at a snobby restaurant that pretty much says "if you don't know what we're talking about, you're not good enough to eat here".
Here are a few I found while looking through cookbooks and the culinary dictionary. Sorted in order of how likely you are to find the term in a cookbook or menu, not alphabetically.
Sauté: Pan-frying or stir-frying. It's cooking something quickly over high heat with some kind of fat in a shallow pan. Probably the first kind of cooking done to justify the invention of a skillet. "Oog, just boil it in a pot like everyone else." "Eela, that's what they said when someone boiled something instead of roasting it on a stick."
Simmering: I do this a lot. It is maintaining the temperature of your cooking liquid about ten degrees below the boiling point. It is not boiling. You may get tiny bubbles coming up through the liquid, but not the big bubbles that a boil produces. The easiest way to produce a simmer is to boil first, then reduce the heat, but some recipes tell you not to.
Poaching: About twenty degrees below a simmer, when the liquid is wavy but no bubbles have appeared. This is for something delicate that you never want to get to a boil because it will get tough or overcook, like fish or asparagus. It is also a good idea when using alcohol in the liquid, because boiling or even simmering will cook off the alcohol too fast. The only way to do this right is to pay attention, which is why poaching is often mentioned on a menu if that is the cooking method used. Bragging.
Blanching: Cooking something briefly in boiling water or oil just to get it partly cooked. This may be because the item cooks at a different rate than the rest of the dish. It can also loosen the skin of a tomato for easier peeling. It is often followed by an ice bath to stop the cooking.
Adjust seasonings: I really dislike when cookbooks resort to "adjust seasonings to taste". What they usually mean is that you're probably going to want more salt or pepper than they have listed, but they can't bring themselves to put that much in the recipe. There are other adjustments you can make, if you know what you're doing. Too much salt, add potato starch or sugar. Too sweet, add lemon juice if it's something that can take it. Too hot, add something creamy. Too bland, try a dried herb before resorting to something hot. There are many adjustments out there, and you can feel free to experiment.
Broth vs Stock: We use these as interchangeable, but they technically have different definitions. A broth is pretty much anything you boil in water to extract its flavoring and essence. It is often seasoned with salt, pepper, or herbs. Stock is a classic culinary term with specific proportions of meat, bones, and mirepoix (a specific combination of onion, celery, and carrot). It is made in a certain way and takes on the characteristics of how long you brown the bones, what parts of the animal you use, etc. It is almost never seasoned with salt. Stock is then strained and used as a base for classical sauces.
Chiffonade: I kind of went over this in the knife skills post, but the picture wasn't great. It's thinly sliced strips of a leafy veggie or herb. While important for a cook to know, it's only important on a menu so the cook can brag. It's a "look at me, I know what I'm doing!" kind of thing.
En papillote: Usually fish, it's an item bundled with herbs or veggies and often a compound butter, all wrapped up in something like parchment paper and roasted. The result is somewhere between steamed and baked. For a flourish, the paper is usually opened at the table, so you can see the process in action.
Au jus: Probably the most misused culinary term in America. It means "with natural juices". It is an adjective, not a noun. There is no noun "au jus", and every menu that says "served with au jus" makes me cringe. Aside from that, it also refers to juices that have not been thickened, as a gravy would be.
Bloom: There are a couple of definitions for this. Most often, it refers to softening gelatin in liquid. "Blooming" gelatin puffs up and gels in the liquid. The other definition is the white stuff on chocolate that is edible, just not pretty.
Al dente: Italian for "to the tooth". It refers to that chewy quality of pasta that is neither tough nor mushy. In 1950's-speak, it's that point where the spaghetti sticks to the wall when you toss it, but falls off a few seconds later. If it stays there, you've overcooked it. (I don't toss pasta at the wall, I taste it like a normal person.)
Aïoli: Garlic mayo. Seriously, that's all it is.
This post got long in a hurry. We'll revisit this topic when my list of terms gets excessive again.