Other forms: unbinding; unbinds
To unbind is to release someone or something that's tied up. In a fantasy novel, the heroine might unbind the prisoners of the evil ogre and rescue them from his terrifying lair.
The verb bind means to secure or fasten something using rope or another kind of restraint. Unbind is the opposite (you can tell from the "reverse" prefix un-). The famous magician and escape artist Harry Houdini managed to unbind himself in many unlikely situations — underwater, in a straitjacket, and buried in the ground, among others.