These definitions come from Environmental Accounting: Energy and Environmental Decision Making by Howard T. Odum, pg. 288.
Available Energy: Energy with the potential to do work (exergy). [If one has firewood they can cook with it because the potential of the wood to be burnt is still there; after cooking, the same amount of energy exists in the form of heat released into the air, but the wood can no longer be used to do what we wanted it for. Energy must be in an available, or usable form for it to be of worth to us.]
Transformity: The emergy of one type required to make a unit of energy of another type. For example, since 3 coal emjoules (cej) of coal and 1 cej of services are required to generate 1 J of electricity, the coal transformity of electricity is 4 cej/J. [If our dinosaur blood spooner sweats for 100 hours to dig up a barrel, we would want to know the available energy in that 1 barrel, how many hours of sweating could be replaced through the utilization of that fuel to power machinery to do work. Using the solar emergy transformity values for dinosaur blood and liquid motor fuel and knowing the efficiency of fuel-to-work conversion of internal combustion engines we can answer about 4000 sweat hours per barrel for the fuel. But the work when finally done, would also include the spooning to get that fuel, and so be at least with a sweat value of 4100 hours.]
Emergy: (spelled with an "m")—all the available energy that was used in the work of making a product and expressed in units of one type of energy. [When you have your transformities worked out so that you know how much one kind of energy is worth in terms of every other, you can sum up in terms of one type of energy all the available energies used directly or indirectly to create something or to offer a service. That total is the emergy.]
Net Emergy: The emergy yield from a resource after all the emergy used to process it has been subtracted. [First, we take into consideration all the emergy that it has taken to get our spooner online, fed, clothed, sheltered, and with spoon, in terms of dinosaur blood, even if the energy required was and is of many different kinds. Then, if he comes up with more blood than what it takes to put and keep him on the treadmill, that is an emergy gain, a net emergy that will allow society to go around. It depends, of course, upon taking the primary source of energy for granted, such as the dinosaur blood in this case.]
Emergy Yield Ratio: The ratio of the emergy yield to that required for processing. [This is the number of spoonfuls that society has left over for every spoonful of energy required directly and indirectly by our spooner as he spoons.]
Solar transformity: solar emergy per unit of energy, expressed in solar emjoules per joule. [Because sunlight is the great and only form of energy that continually comes from outside the Earth, and because it is the basis of all plant life and thus animal life, the challenge is to calculate the emergy worth of something in terms of present sunlight. The only other energy source affecting us that is not somehow related to sunlight, is a result of the process that gathered together bits of matter from the stars to form the planet Earth and its moon, the energies that are contained in the surface elements of the planet, the uplifting of the continents and the restless tides, the volcanoes and earthquakes.]
Sustainable use: the resource use that can be continued by society in the long run because the use level and system design allow resources to be renewed by natural or human-aided processes. [When we use natural resources at a speed and in a manner which does not diminish them, or use them to create a way of living that can last so that we are not threatened with catastrophe as they do run out, that use can be said to be sustainable. If we do not, then we will be forced to adapt to the condition of less, either by there being less to spread around or by becoming a lesser number of people, or both.]