A TENS machine is a small, portable device which is worn on the body.
The box is attached by wires to sticky pads stuck to the skin.
Small electrical pulses are transmitted to the body, like little electric shocks. This can help to ease pain in some people with certain types of pain.
Although there is not much robust proof that TENS machines work, many people do find them very helpful.
The advantage is that TENS is well tolerated and largely without side-effects.