Thermal imaging is a technology which allows people to take pictures of heat energy. This is a noninvasive and convenient way to inspect certain areas of a home. For example, thermal imaging cameras can detect the heat signatures of pests or help map piping without tearing apart a wall.
Thermal imaging cameras are not actually cameras, but heat sensors. They do not detect visible light.
Thermal Imaging vs. Night Vision
Night vision and thermal imaging are not the same. Night vision sight devices take small amounts of light and magnify it, while thermal imaging only detects heat energy.
Thermal imaging technology can reveal things that the eyes cannot see, and as a result these devices are often used during home inspections. Unfortunately, however, you cannot detect moisture or some types of property damage with a thermal imaging camera.
Only surface thermal fluctuations will be detected by thermal imaging. This is different from X-ray devices, which can "see" through walls.