A foam roller is a cylindrical tool made of dense foam that's used for self-myofascial release and muscle recovery. By rolling different parts of the body over the foam roller, you can apply pressure to tight muscles and fascia, helping to release knots and alleviate muscle tension. It's commonly used to improve flexibility, reduce soreness, and enhance blood circulation. Foam rollers come in various sizes and densities to cater to different needs and levels of pressure. They're popular among athletes, fitness enthusiasts, and individuals seeking to improve their overall muscle health.