is a lightweight
 elastic band used to induce muscular contraction. This contracting motion
 builds strength in the muscles as the user pulls against the band. Resistance
 bands have been around in some form or another since the early 20th century. At
 first, they were primarily used for rehabilitation. Those with damaged muscles
 would use the bands to recuperate their lost strength

Benefits & Features

Using these elastic or fabric bands to add tension or resistance during exercise makes it more difficult to do movements, and engages more muscles, which helps to build strength, as recommended by the CDC(opens in new tab).
"Resistance bands recruit the 'stabilizer' muscles   this muscle group is significant because it supports our larger muscles and joints when we move, and helps reduce the risk of injury. So they are a safe and low-impact option for older people, and are often used for rehabilitation."

Exercise Bands