Definition: E & M
(1) (E&M) (Entertainment & Media) An umbrella term for radio, TV, movies, online and print publishing.
(2) (E & M) (Ear & Mouth) Also known as "rEceive & transMit" and "earth & magneto," E & M is an early telephony term for signaling. A voltage would be applied to the "mouth" lead of the circuit, which signals the "ear" lead at the other end. There are a variety of two-wire and four-wire E & M signaling methods used between PBXs and network connections throughout the world.