A wart is a lump of abnormal skin growth that is caused by a virus. Depending on where they are, they can be painful. Some warts go away by themselves fairly quickly, others need to be removed by applying acid or by freezing them or cutting them off.
Something that looks like it has warts is described as warty. Toads look very warty, and so does the gourd in the picture.
An X-ray machine lets doctors take pictures of the bones inside your body. X-rays are a special kind of light which go through all of your body except your bones and other hard parts of your body, so the bones show up as white on the X-ray and the muscle in between shows black.