'energy-efficient' originates from the combination of 'energy' and 'efficient', where 'energy' refers to the capacity to do work and 'efficient' means achieving maximum productivity with minimum wasted effort or expense.

'energy-efficient' evolved from the increasing need to describe products and systems that use less energy, especially in the context of environmental conservation.

Initially, it meant 'using less energy', and this meaning has remained consistent as awareness of energy conservation has grown.