Tandoori chicken - a Punjabi dish - is so-called because it is cooked in a round, deep clay oven called a tandoor, as are other tandoori meats, kebabs and bread. Meats are usually first marinated in yoghurt and spices . The traditional glorious red or golden colouring is from colourants - often dried, ground beetroot for red.
The tandoor is a very hot oven using charcoal for heat.
Similar ovens have been, and still are, used around the Middle East and Asia for centuries.
Tandoori?
It is a method of cooking - a tandoor is a large clay oven that has a lid rather than a door - in shape and size it is similar to a large amphora. Hot coals or charcoal is placed in the bottom to heat it.
It is common to large parts of India.