1. energy savings - Using less than you did before the 'saving measures' were adopted
2. energy use/consumption - Converting one type of energy into another in order to carry out work
3. energy efficiency - Using the smallest amount of energy necessary to do a job
4. my preferred term is energy use reduction
5. using energy - Converting one type of energy into another in order to carry out work
6. wasting energy - Using more energy than is required to do the job
7. carbon saving! - Reducing the amount of 'carbon' emitted whilst doing a job
8. smart meter - Like a normal energy monitor but one that makes it easier for a lay person to understand the concept of energy use
9. smart energy monitoring - As above really
10. ...............

1. energy savings: Reduction in energy use compared with 'the old way', often expressed as a percentage. No guesswork allowed (e.g. calculating individual savings from national averages).
2. energy use: consumption kWh from grid + kWh microgeneration + calorific value of all fuel
3. energy efficiency: The ratio of useful work to energy consumed. But even when comparing similar things (e.g. LED and incandescent bulbs) it's very difficult to define 'useful work' technically, let alone socially.
4. my preferred term is energy use reduction: I have no problem with 'energy savings' provided the term is not abused or hyped. See (1)
5. using energy: Consuming energy resources in any way, however technically inefficient or morally despicable. See (6)
6. wasting energy: Consuming energy resources in a way which is either technically inefficient or socially unjust. So is a solar-heated outdoor swimming pool OK? Heh heh!
7. carbon saving!: REALLY IMPORTANT. But tricky and easily-spun, especially when biomass or embodied carbon is involved. Always ask how the alleged saving is calculated.
8. smart meter: A meter which can be used for real-time demand management. Demand management is essential for a renewables-based grid, but consumers will want fair, comprehensible tariffs - not "we will charge you what we like, when we like".
9. smart energy monitoring: Obviously a relative term, but I suggest that electricity monitoring is not smart unless it is appliance-by-appliance. 'Smart' heating controls are mainly a sticking-plaster for poorly-insulated properties.

I am going to have a crack at this, though I agree with Ed, it is mainly contextual (that is right click on a PC application isn't it), but I shall limit it to electrical usage.

1. energy savings: Using less overall, regardless of efficiency.
2. energy use/consumption: Just the overall amount you use, the MJs, may or may not be in a set period of time
3. energy efficiency: Doing more work for less energy input
4. my preferred term is energy use reduction: No idea
5. using energy: Having something switched on
6. wasting energy: Leaving it switched on when there is no need
7. carbon saving!: One measure of generation efficiency that takes primary energy into account
8. smart meter: Just a meter that time stamps and may possibly allow for some control
9. smart energy monitoring: What my CurrentCost and Raspberry Pi does, can have a display that quickly and clearly shows that is happening.

10. Price, Cost and Value of Energy: This is hard, Price is the just the monetary term in £ per agreed unit (Usually £/W), Cost is the indirect and often non-monetary 'things' like resource depletion, loss of natural capital etc. Value is the benefit of using (or not using) something. Take a hospital, they are very energy inefficient, but overheating a ward is probably more cost effective that allowing patients to die of hypothermia.