Surgery operates directly on the physical body. There are virtually no surgeons who are proficient in all types of bodily surgical interventions. Due to the ever increasing refinement of the knowledge of the physical body, ever more specialized forms of surgery emerged. Some examples are the fields of vascular surgery; orthopedic surgery; oncological surgery; neuro-surgery; ophthalmology; oral surgery; cosmetic surgery, to name but a few. But the well-known Cesarean section at birth (delivery by the abdominal wall) is a form of surgery, practiced by the gynecologist.
In short, surgery means a direct invasive intervention on the physical body. This is on the one hand targeted towards emergency care, but also towards planned care. For example, a cardiac heart arrest may require emergency surgery, while other types of surgery may be planned months in advance.