My son has developed bone cancer. What is it exactly?

Adult or child? Cancers that develop in bonse are only common in late adolescence and early adulthhod: osteosarcoma and chondrosarcoma, and most commonlyaround knees. Ewings sarcaoma, and many other tumors affect bones, but usually are not of bones. Adults most commonly have disease from may other places that effect bones: prostate and lung cancer lead the pack, and multiple myeloma destroys bones. No more room.
Try to get details. Specifically, bone cancer is a type of sarcoma. It is more common in children/ young adults and usually one hopes to detect it early enough that surgery and / or radiation would be helpful. Other confused diagnoses with this term improperly used are cancers that start someplace else and spread to the bone (breast cancer for instance) or cancers of the bone marrow (leukemia).