Element Zero is an element found used to enable Faster-Than-Light travel in the Mass Effect Universe. When subjected to electrical current Element Zero emits a dark energy field that raises or lowers the mass of all objects within it. This "mass effect" is used to generate artificial gravity, manufacturing high strength conscruction materials, and enabling faster-than-light(or FTL) space travel. Humanity discovered refined element zero at the Prothean research station on Mars, allowing them to create mass effect fields and develop FTL travel.
As written in the Mass Effect 2 codex, Element Zero is created when solid matter, such as a planet, is affected by the energy of a star going supernova. The material is common in the asteroid debris that orbits neutron stars and pulsars. These are dangerous places to mine, requiring extensive use of robotics, telepresence, and shielding to survive the incredible radiation from the dead star. Only a few major corporations can afford the set-up costs required to work these primary sources."