Musculoskeletal refers to the muscles, bones, joints, ligaments, tendons, nerves, cartilage, fascia, and bursas that make up the body. Effectively anything that is not the blood vessels, viscera and brain.
Musculoskeletal injury or pain is what we deal with almost all of the time.
This covers Sports Injury and concerns everything from a bad back or neck, a painful shoulder, tendon strains, muscles sprains, torn ligaments and joint pain. Arthritic and wear and tear conditions come under this as do nerve related issues. Most conditions have a number of different components. For example a sprained ankle can often have tendon, ligament and nerve damage all in one.
The links on the right give access to more detailed descriptions.