Qpel

Quarter pixel (also known as Q-pel or Qpel) refers to a quarter of a standard pixel. It is used in many modern video encoding standards such as MPEG-4 ASP and H.264/AVC to refer to quarter pixel precision in motion estimation and motion compensation. Though higher precision motion vectors take more bits to encode, they can result in more efficient compression overall, both through the decreased bit cost of the residual and the increased quality of the macroblock.