Tadka is the process of heating oil or ghee and infusing it with spices, herbs, and aromatics like garlic, chillies, or hing (asafoetida).
The cooking process shows the traditional egg bhurji recipe, with the street food vendor heating oil in a pan and sauteeing finely chopped onion, green chilli, and ginger.
Tempering, or tadka, is the final flourish. It is when you heat oil or ghee, throw in whole spices and aromatics, and pour it over a finished dish.