Cupping is a technique used to reduce pain that originated from Eastern medicine, mainly China. In traditional Chinese medicine, a vacuum is placed in the cups on the body in specific locations to influence the flow of the qi in the body which promotes healing.
Sometimes, physical therapists may use cupping as a technique to increase blood flow to different muscles/tissues in the body. They can also use the cups as a form of feedback with certain movements to improve body awareness or posture. I use cupping in my practice and have found great results.