Yogurt is made from fermented milk and has a great many uses. It can be consumed as a drink (such as the Indian lassi) or eaten as a kind of relish (such as the Indian raita, a cooling mixture of yoghurt and cucumber), or made into a kind of cheese (such as labneh). It can also be used as a dressing or as a marinade to tenderise meats, as in tandoori chicken.
In western Europe yoghurt is perhaps most popular as a sweetened, fruity dessert or breakfast food. Yoghurt can be made from the milk of cows, sheep, goats, even mares, camels and female yaks; each has its own flavours and cooking properties. It's often used in northern Indian curries to give flavour and ure and to temper the heat of chillies.
Yoghurt is very digestible, even to people with lactose intolerance. It's also seen as a 'healthy' food in many parts of the world. Yoghurt can be used as a replacement for cream or crème fraîche in most recipes. It's available with a wide range of fat contents, from full-fat with added cream to very low fat.
Yoghurt with a very low-fat content has a tendency to curdle when used in hot dishes, though, so allow the dish to cool first and don't let it boil once the yoghurt is added.