The term 'Separate Grain from Chaff' is a metaphor for the process of winnowing, which is a method of separating grain from chaff. Winnowing is an ancient technique used to remove the husks and other inedible parts of grains from the edible parts. The process involves throwing the mixture of grain and chaff into the air so that the wind can blow away the lighter chaff, leaving the heavier grain behind. This process is still used today in many parts of the world to separate grain from chaff.