The dream body is the image one has of his/her own body in his/her dreams. Our dreams usually feature our real bodies, since we expect it to be there.
Our dream body is nothing more than the representation of our body image in dreams. Our brain uses our spatial perception to figure out where our body is located, so that we can displace better. This notion is also carried into our dreams, since we usually don't know we are dreaming.
Our dream body is usually the same as our real body; but that is no rule. We can become anything in our dreams, but shapeshifting, as it is called, is more easily done in lucid dreams, since our consciousness has control over the dream.