According to the University of Maryland Medical Center, cartilage is located in the nose and ears, as well as several of the body's joints, including the knees, hips, shoulders and fingers. Cartilage is one of the body's chief connective tissues. It takes the form of a matrix and contains proteins, sugars and collagen. Wikipedia notes that cartilage is also found in intervertebral discs and the bronchial tubes.
The University of California, San Francisco describes articular cartilage as a firm, rubbery material. While it is durable, repetitive use can cause it to wear out. This problem frequently manifests in the knees. Approximately 6 million people per year suffer from damaged knee cartilage. Wikipedia states that cartilage has a limited capacity for healing or repairing itself. To discover damage to the area, doctors must first inject dye into the synovial membrane before taking an X-ray. This is necessary because cartilage does not usually show up on X-rays.
The University of Maryland Medical Center explains that some people ingest supplemental cartilage to help with a variety of ailments. While researchers were initially hopeful that ingesting the cartilage from sharks could be helpful in battling cancer or in repairing or growing new cartilage, there has been no scientific evidence to prove that it does.