Compare the input work and output work?

it is compared with efficiency which can never be 100% due to friction and gravity.

Input work is any work done on the system by the surroundings which in a reaction is endothermic. This is because work and energy are interchangeable and the system will store the energy. Output work is work done by the system on the surroundings and is therefore exothermic, because the work/hear is being put onto the surroundings (i.e surrounding universe not involved in the reaction).