Surgical excision of dead, devitalized, or contaminated tissue and removal of foreign matter from a wound.
Not a nice experience for either the nurse or the patient. For the patient, feeling someone poke and scrape at a large open wound can be quite nauseating and/or painful. For the nurse, making sure you clean the wound properly without hurting or damaging the patient can be tricky.
Trivia: When I sustained a compound fracture of my left leg a few years back I had to have the wound debrided several times. There was a student nurse looking on; in my morphine induced state of unreality, I decided to have some fun. The wound was deep and exposed tendons, muscles and some bone. I flexed the muscles in my leg a little - The poor student nurse made a nice "eep" noise and fainted dead away. (When you cannot think straight from being drugged, stuff like this is the height of hilarity.