Mass effect fields are created through the use of element zero. Element zero can increase or decrease the mass content of space-time when subjected to an electrical current via dark energy. With a positive current, mass is increased. With a negative current, mass is decreased. The stronger the current, the greater the magnitude of the dark energy mass effect.
In space, low-mass fields allow FTL travel and inexpensive surface-to-orbit transit. High-mass fields create artificial gravity and push space debris away from starships. In manufacturing, low-mass fields permit the creation of evenly-blended alloys, while high mass compaction creates dense, sturdy construction materials.
The military makes extensive use of mobility enhancing technologies, with mass effect-utilizing fighting vehicles being standard front-line issue in most military forces. The Mako's small element zero core can reduce the vehicle's mass enough to allow a safe drop from the Normandy. Mass effect fields are also essential in the creation of shields to protect against enemy fire on the ground, and protect starships in planetary orbit or during space battles.
Many biotics can also use mass effect fields which are biologically generated and controlled. This requires intensive training, and cybernetic implants, but can produce impressive offensive or defensive effects. Some biotics' talents are not strong enough to be offensively viable, but all biotics are sensitive to the presence of mass effect fields.
However, the use of mass effect fields creates static electrical charge. In starship drive cores, this charge must be grounded at regular intervals, either by touching a planet surface or interacting with a planet's geomagnetic field, to prevent the electricity discharging into the hull and causing catastrophic damage. For biotics, this manifests as an occasional static shock when they touch metal or other people.