The efficiency of a machine refers to the ratio of work output to the work input as a percentage.
The efficiency of most machines is less than 100% because some work is lost due to friction and heat.
Therefore, a machine with high efficiency has less wastage of energy due to factors such as friction of the moving parts. Conversely, low efficiency means there is more wastage of energy.
Plasma...I believe is always a good conductor of electricity. I was tempted to say a solid, but not all solids are the same in composition and that goes for liquid and gas as well.
