A deformity is a condition in which part of someone’s body is not the usual shape — a bone, a joint, the spine, a limb — often from the way it grew, from injury, or from illness. Doctors use it as a calm technical noun: they name a specific deformity and talk about treatment. In older writing it also meant ugliness in a looser, ruder way; that use has mostly faded, and it was never kind. You can also hear it, a little stretched, for a badly made object (“a deformity in the casting”), but the home meaning is the body. It is formal. Everyday English may say a birth difference, a bent back, or name the exact condition instead. Handle the word gently: it describes a shape, not a person’s worth.