A back massager for a chair is a padded mat or cushion with built-in motors and rollers that straps onto most office, car, or lounge chairs to deliver targeted massage while you sit. It typically offers modes like kneading, rolling, vibration, and heat to loosen tight muscles along the lower and upper back, shoulders, and sometimes the seat. Powered by AC or car adapters, it’s designed for hands-free use during work, driving, or relaxation without needing to lie down. It’s a practical option for daily tension relief if you spend long hours seated.