Surgery is a medical procedure where doctors cut into the body to fix something that's wrong, remove something harmful, or repair damage. A surgeon might operate on a broken bone, remove an infected appendix, repair a damaged heart valve, or reattach a severed finger.

Modern surgery requires years of training because surgeons need to know exactly where everything is inside the body, how to cut safely, and how to help tissues heal properly.

Surgery has changed dramatically over time. Two hundred years ago, operations were terrifying ordeals performed without anesthesia (medicine that makes you unconscious and unable to feel pain). Patients had to be held down, and many died from infections afterward because doctors didn't understand germs. Today, anesthesia keeps patients comfortable and asleep, while sterile techniques prevent infections. Some surgeries now use tiny cameras and instruments inserted through small cuts, letting surgeons work inside the body while watching a screen, which can mean faster healing for patients.

People also use surgery more loosely to mean any major fix or overhaul, like when someone jokes about needing “emergency surgery” on their messy bedroom.