A malformation is when a part of the body did not grow in the usual shape. Doctors use it for a bone, an organ, a hand, a heart — something that formed in a wrong way, often before a baby is born. It is a careful hospital word, not a playground word. You hear it in reports and from doctors, not much in daily chat. Though actually, people sometimes stretch it for things that are not bodies at all, like a plan that was put together badly; the body meaning is still the main one. It names the problem itself (a malformation of the spine), not the person.