Biotics are rare individuals with the ability to create and manipulate mass effect fields. Given the correct implants and careful training, a biotic can raise defensive barriers, yank opponents off their feet, or shred an enemy apart at the molecular level.
A biotic gains these abilities after exposure to dust-form element zero in utero, or via secondary exposures at a young age. Though this often results in fatal cancer, roughly 10% of those exposed develop element zero nodules along their nervous system. Once activated by the body's electrical impulses, these nodules allow the biotic to create mass effect fields, though most need a neural implant to wield them effectively.
Some species, like the asari, are naturally biotic, but human biotics are still relatively rare and many view them with suspicion. The Andromeda Initiative has proven attractive to biotic applicants.