We can't all be Julia Child, but you can at least understand her recipes with these definitions. I recently read What's a Cook to Do? by James Peterson, an awesome guide to cooking techniques. I don't think you need all 484 terms, but you can at least try out these techniques in your own kitchen and save the fancy cooking terms terms for impressing your friends.
Poach
To gently cook a food in simmering liquid. This isn't to be confused with boiling, which is done at much higher temperatures and with vigorously bubbling water. Poaching is great for delicately cooking proteins like chicken, fish, or even fruit.
#SpoonTip: When poaching an egg, add a little bit of vinegar so all the egg bits stay stuck together.
Butterfly
Butterfly is a more elegant term for cutting a piece of meat almost all the way through lengthwise, and leaving the two halves connected in the middle. This way of opening up a thick cut of meat ensures that more of it is exposed to heat and it will cook more evenly. Plus, the mental image of butterflied chicken is hilarious.
Blind bake
No, it's not the latest cooking competition. Blind baking is when you bake a pastry base or crust partially or all the way before adding filling. This helps keep the bottom of your crust from getting soggy, or makes sure you have a crunchy crust when you add an filling you don't plan to cook.
To keep your pastry from puffing up in the middle, cover the top of it with aluminum foil and then add dry beans or rice to weight it down. Pricking it all over with a fork can help let the steam out and keep your crust even as well, but don't do it so much that your filling leaks out.
Chiffonade
French for "little ribbons," this technique sounds like it has more to do with dresses than cooking. You take your herbs, or heck, your omelet or crepes if you want, stack them and roll them tightly, and then slice across the roll to get narrow strips. It's great for chopping things like lettuce for salad or making garnishes. Chiffonade basil for an Insta-worthy caprese salad.
Mise en place
Mise en place is another French term, meaning "to put in place." Chefs use this to put all of their prepped ingredients in bowls beforehand, so when it's time to start cooking they just have to combine them. If you feel like washing tons of extra dishes is worth Food-Network levels of organization, go for it.
Fold
Okay, this one doesn't sound that fancy, but it's tricky in practice. Folding is a way to gently combine a heavier ingredient into a lighter one, like egg whites. Using a spatula, you lift the ingredients from the bottom and "fold" them over the top. This helps prevent over mixing, because there's nothing tasty about tough pastry and flat soufflés.
Broiling
Broiling is cooking directly under an exposed heat source at high temperatures. Or, it's discovering the broil setting on your oven and sticking whatever you want to cook right under the top component. This is good for finishing dishes if you want to get a nice browned crust on meat, or bubbly cheese on a casserole.
You can also oven broil meats and vegetables, but make sure you're watching. Because broiling requires very high temperatures, your food can burn quickly. For those of us who don't have kitchen torches (i.e. mini-flamethrowers), broiling is how you get that crunchy sugar goodness on top of a creme brulee.
Blanch and Shock
No, this is not just what happens when you get your midterms back. Blanching is when you put food, usually a vegetable, into salted, boiling water for a short amount of time. After you blanch your veggies, shocking is throwing them into a bowl of ice and cold water. This stops them from cooking too much and getting mushy, and makes sure your green beans or broccoli stay a nice, bright green. The combination lets you cook veggies just a little while still maintaining flavor and crunch, and can also help remove peels.
Roux
A roux ("roo") is a thickener made by combining equal parts flour and fat, usually butter. You whisk them together in a pan and cook over medium heat until the combination starts smelling toasty. Depending on how long you cook them, you can have a white roux, a blonde roux, or a dark roux. The longer you cook a roux, the nuttier the flavor and darker the color. You can add them to thicken soups and stews, and roux is the key to making a killer homemade mac and cheese.
Al dente
With the rather unappetizing translation of "to the teeth," this Italian phrase describes the ultimate Italian dish: pasta. At its simplest, it just means cooking pasta just until done so it still has a firm texture. There's nothing tasty about limp noodles. While most pasta boxes offer instructions for cooking al dente, I find the best method to take a piece of pasta out periodically during cooking, run it under cold water, and try it until you get the right texture. Bonus: Al dente pasta has a lower glycemic index than pasta cooked longer