Sella rice is more commonly known as parboiled rice. After harvesting, while its husk (the brown covering on the grain) is still on, it is subjected to some form of heat processing that helps it to be partly cooked while still in the husk. Later, the rice is de-husked. Due to the moisture and heat involved, it has a mild yellow colour and a very characteristic taste that makes it a favourite for rice preparations like pilafs and rice puddings.
Steamed rice, on the other hand, is rice that has been cooked either in a pressure cooker, a vessel or a microwave with water, thereby using steam to cook it completely. Indeed, steaming rice is so common in parts of India that most cooks do it without any accurate measurement of water or rice.