E-Ink, or Electrophoretic-Ink, is the technology that makes Electronic Paper Displays (EPDs) possible.
Unlike other display technologies, such as LCD or LED, E-Ink uses no backlighting. This allows E-Ink based applications to use far less power than other display types. Furthermore, E-Ink-EPD displays can operate for weeks without recharging on small, lightweight batteries, which means thinner/lighter display panels.