What is Infrared?          
Infrared energy is part of the electromagnetic spectrum and behaves similarly to visible light. It travels through space at the speed of light and can be reflected, refracted, absorbed, and emitted. Other common forms of electromagnetic radiation include radio, ultraviolet, and x-ray.
What is Infrared Thermography?
A regular camera takes pictures of what we see from visible light. A Infrared camera takes pictures of the invisible infrared light/heat radiation. For a more techy answer, go here. Infrared Primer
(above- a ceiling in a house showing insulation lacking in spots)
What is the difference between and Energy Audit and a Thermal Audit?
With an Energy Audit someone comes in and rates all the major energy consuming appliances to determine energy efficiencies. They may or may not put your house under negative pressure to help find air leaks. Personally, I believe that you understand an old furnace or an old fridge are less efficient than new ones and that buying new ones will be more energy efficient.

With a Thermal Audit we will be using the Infrared Camera to "see" what is inside/behind the walls and ceilings. Also we will be putting your house under a negative pressure. This will show us thermally where the cold air is coming into your house. This air will show up as dark wispy areas. The U.S. Department of Energy suggests that every $1 invested in an energy improvement project can yield $4 to $7 in energy cost savings over the life of the improvement. Thermographic Audits can help you identify opportunities that can save you hundreds of dollars in energy costs.

Water intrusion: Thermal imaging can reveal excess moisture due to plumbing leaks, roof leaks, leaks around windows, etc.  Wet areas of building materials cool when energy is transferred during the water evaporation process; therefore, a wet (“cooler”) area will stand out from the surrounding dry (“warmer”) surface.
Roofing leaks: scanning roof coverings can reveal water intrusion and accumulated moisture below the surface. Due to its thermal properties (high thermal capacity), water typically gives up heat at a much slower rate than the surrounding roof materials. The areas of accumulated moisture can therefore be detected when scanning the roof surface.  This type of roof inspection is best done in the evening or early nighttime after thermal energy imparted during the daytime is transferred or released..