TENS is electrotherapy and one of the physical therapies used by physiotherapists.
The acronym TENS is the short name for Transcutaneous Electrical Nerve Stimulation (T.E.N.S.).
The first TENS unit was invented by Australian physiotherapist, Mr Jim Lamers in 1971. He coined the term "TENS" in 1972. The rest of the world has since adopted the acronym - and TENS has become a generic term for both the therapy and the devices.