Surgery (from the Greek: χειρουργική cheirourgikē, via Latin: chirurgiae, meaning "hand work") is an ancient 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, or to help improve bodily function or appearance.

An act of performing surgery may be called a surgical procedure, operation, or simply surgery. In this context, the verb operate means to perform 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. Persons described as surgeons are commonly physicians, but the term is also applied to podiatrists, dentists (known as oral and maxillofacial surgeons) and veterinarians. A 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, or veterinarian.