What we think of as "curry" are dishes that have been cooked with curry powder, typically with pre-mixed flavors of turmeric, ginger, chillies, and coriander, among others.
But these dishes would be almost unrecognizable in India, which uses much more diverse blends of spices (masalas) in its dishes, all individually prepared and added as you cook so that the mixture is unique and varying depending on the region and sometimes by specific kitchen.
Put simply, "curry" is a massive oversimplification of Indian cuisine.
We can thank the British for what we think of as "curry." They coined the term back when Imperialism was still strong, and it most likely stems from the dish "kari," which is a type of spicy gravy Indian dish with sauce ladled over meats. For example, "Kozhi Kari" roughly translates as chicken with gravy.
But in India, not all "karis" are called "kari."
"In North India, the rich, sauce-heavy dishes we might call 'curries' go by many different names," Laura Siciliano-Rosen, the co-founder of Eat Your World, explained to Business Insider. "Butter chicken, kadhai paneer, mutton korma, saag chicken, and so on."
So if you want to try and make authentic Indian kari, a few of the key spices to have on hand are turmeric, garam masala, cumin seeds, coriander power, cinnamon, red chili or cayenne powder, cardamom, ginger, garlic, and mustard seeds. Don't be afraid to branch out and experiment.
And if you want to order authentically Indian dishes the next time you're at a restaurant, stick to dishes without "curry" in the name and look for palak paneer, saag chicken, or mutton korma. Order a side of roti and dip it in your extra sauce.
That doesn't mean you can't use your curry powder when you're cooking - it's delicious in salad dressings and some soups - just realize that it's not an authentic part of Indian cuisine.