It is energy efficient when we use less energy to achieve the same result.
Example: insulating a house means that less energy is needed to heat a house to the required level. Replacing an old boiler with a more efficient version means that less fuel is used to provide the amount of heat you need.
Example: we can improve energy efficiency by making changes to how we do things like turning off lights and electronics when we are not using them.
You can find out more about energy efficiency in your home at www.seai.ie/home-energy/