Debridement is a term often used in the medical field when something is being removed. This could be skin, dead tissue around a wound, a bone lesion, or as in your wife's case loose fragments of cartilage.
The surgeon will try to stitch down any flaps of cartilage. If that's not possible the torn cartilage is carefully scraped away until there is just normal cartilage showing.
The operation is usually very successful in eliminating pain, swelling, and giving way of the knee. Most people have increased function as a result of these improvements.