What's the difference between passive matrix and active matrix?
From Wikipedia:


  [In active matrix,] each pixel is attached to a transistor and
  capacitor actively maintaining the pixel state while other pixels are
  being addressed in contrast with the older passive matrix technology
  in which each pixel must maintain its state passively, without being
  driven by circuitry.


In other words, in passive matrix (PM), each pixel is addressed by a row-col scheme one by one with high rastering frequency. PM is incapable of maintaining its state (on/off) while other pixel on the same row/col are being switched, so high frequency scanning and high intensity lighting are required, resulting in high power consumption due to ohmic losses. In active matrix, each pixel is capable of maintaining its state while other pixels are being addressed thanks to extra circuitry, and for this extra circuitry it's called "active".