Tempering
The English word for tadka: heating whole spices in fat so their flavour passes into the oil.
Also: spice tempering, seasoning oil, tarka in English, chaunk
In English-language cookbooks, tempering usually means tadka, the practice of heating whole or coarsely cut spices in oil or ghee. The word is borrowed from metallurgy, where tempering controls hardness, and cooks use it for controlled heat applied to flavour. Order matters: mustard seeds go in first and pop, followed by cumin, then curry leaves and chillies, and finally powdered spices or asafoetida for a few seconds. The fat should be hot, but not smoking. A tempering can come at the start of a dish, as a base, or at the end, as a garnish poured over, which gives a bright top note. The same idea appears in Persian and Turkish cooking.