In medicine, traction is the act of pulling on bones or limbs in a certain way to help with healing. An arm in traction is temporarily tied up, but it is probably on the mend.
A person in traction is presently immobile, but traction can also be used to describe the state of an object being pulled, or the friction between that object and the surface it is pulled across. Traction can also refer to something or someone that has picked up movement, like an idea or a candidate. If your idea for chocolate covered onions has gained traction, it is becoming popular; if it has lost traction, people have come to their senses.