It means how much input work you put into the machine, which then becomes output from the machine. So you're putting 80% of work into the machinie. To find the efficency of a machine, it's output divided by input work.
efficiency is the ratio of the power ouput to the power input
Explanation:
It compares how much energy is used to do work versus how much is lost or wasted to the environment, the more efficient the machine, the less energy wasted.
