Surgery (from the Greek: χειρουργική cheirourgikē, via Latin: chirurgiae, meaning "hand work") is a medical specialty that uses operative manual and instrumental techniques on a patient to investigate and/or treat a pathological condition such as disease or injury, to help improve bodily function or appearance, and sometimes for religious reasons. An act of performing surgery may be called a surgical procedure, operation, or simply surgery. In this context, the verb operate means performing surgery. The adjective surgical means pertaining to surgery; e.g. surgical instruments or surgical nurse. The patient or subject on which the surgery is performed can be a person or an animal. A surgeon is a person who performs operations on patients. In rare cases, surgeons may operate on themselves. Persons described as surgeons are commonly medical practitioners, but the term is also applied to physicians, podiatric physicians, dentists (or known as oral and maxillofacial surgeon) and veterinarians. Surgery can last from minutes to hours, but is typically not an ongoing or periodic type of treatment.

The term surgery can also refer to the place where surgery is performed, or simply the office of a physician, dentist / oral and maxillofacial surgeon, or veterinarian.