When it comes to trying to define "to be energy efficient" or "energy efficiency", there does not seem to be a single commonly-accepted definition of energy efficiency. it is generally thought that an increase in energy efficiency is when either energy inputs are reduced for a given level of service, or there are increased or enhanced services for a given amount of energy inputs.
There are many ways of saving energy.
I can turn down the thermostat and put on a sweater. or use a programmable and ignore the setting by wearing more clothes. My bill drops a number of BTUs.
I can take a military shower. Water on, wet down, Water off. Soap up, scrub. Water on Rinse off, water off. In 90 degree F water of course. My bill drops a number of BTUs. and my water bill drops.
I can add some insulation to the house. Leave the thermostat setting the same. My bill drops a number of BTUs.
I can install a tankless hot water heater. The bill drops a few BTUs and my water bill stays the same.
You can change the way people work.
You can change the way things work.
I believe 'Conservation' is the way people work.
I believe 'Efficiency' is the way things work.
As an Energy Auditor, I can explain to people how the conserve. They have to make the choice. They have to make it a habit. I'm not going to follow them around and watch to see they are doing it.
Very much like my physician telling me to eat less, get extra exercise and not to use as much salt. All on me.
As an Energy Auditor, I can recommend how people can improve their homes to increase efficiency. They have to buy the stuff (and pay for or provide the labor) to improve their home.
The Dr. wants me to change my habits, and energy conservation is changing my habits.
Efficiency is something that changes energy consumption without requiring more then a one time purchase or install to change how things work.
Both are important. One is less expensive in $$. One is less stressful to remember.