High efficiency (HE) refers to products or systems using less energy to do the same or better job than conventional products or systems.
High efficiency saves energy, save money on utility bills, and helps protect the environment by reducing the amount of resources and power (and associated environmental impacts) that needs to be generated.
Examples that come to mind include HE washing machines, fuel efficient vehicles, and HVAC systems.
As utility prices and environmental sensitivities increase, these high efficiency products become more and more popular.