What is the difference between high efficiency and low efficiency?

Efficiency describes how well a device transfers one form of energy to another form of usefull energy. High efficiency transforms most of the energy with very little loss. Low efficiency only transforms a small amount into usefull energy and the rest is usually lost to heat energy from friction. For example, a car is a low efficiency device because only a small amount (I forget the actual number. Probably around 50%) of the chemical energy in gasoline actually gets converted to energy of moving the car. The rest is lost to air resistance, friction between all the moving parts & and unused heat out the exhaust pipe.