Transcutaneous electrical nerve stimulation

A transcutaneous electrical nerve stimulation (TENS or TNS) is a device that produces mild electric current to stimulate the nerves for therapeutic purposes. TENS, by definition, covers the complete range of transcutaneously applied currents used for nerve excitation, but the term is often used with a more restrictive intent, namely, to describe the kind of pulses produced by portable stimulators used to reduce pain.

Source: Wikipedia — Transcutaneous electrical nerve stimulation (CC BY-SA 4.0)