Terrigenisis is the process in which an Inhuman is given their powers. It involves a Terrigen Bomb releasing the Terrigen Mist from its crystal, which in turn activates the powers of an Inhuman or Inhumans in the Terrigen Chamber.
The process of power giving is random, leading to some unfortunate cases where the Terrigen Mist deforms an Inhuman, by warping their appearance, alongside a new power.
Vijay Nadeer is a loose thread in the MCU from Agents of S.H.I.E.L.D. leftover from before the series. He currently remains in a Terrigen cocoon in the ocean.