Night Vision means the ability to see at night. Infrared is a color that humans can't see. It's used in imaging because it's invisible. FLIR is Forward Looking InfraRed. It differs from "Infrared imaging" in how it is "performed." Regular Infrared Imaging has an infrared sensor to pick up the light, while an Infrared light bathes the scene in infrared light. FLIR differs from the above in that it doesn't actually add any infrared light to the scene, only that it tries to pick up and process the infrared to form an image.
Thermal Imaging is a way of detecting the heat signatures which come off different physical items. The Thermal Imaging doesn't see light, but rather sees heat.
Remember that these cameras don't actually see light the same way you or I do. You and I see the colors Red, Orange, Yellow, Green, Blue, Indigo, and Violet. Once you start talking Infrared, or Thermal heat, you're not talking about colors that we can see. So if you're going to use something like that for a video, you're going to get a computer rendered representation of what the scene looks like, not what the screen really looks like.
In applications where there is no distinction between night and day and lives are at risk, like in the military, it is important to establish visibility without being visible yourself. For this night vision goggles were created. Night vision goggles work by collecting what little amount of light is available and amplifying it so that it can be discerned by the naked eye. Infrared is a new technology employed with night vision goggles. Rather than employing visible light and amplifying them, infrared goggles rely on infrared waves that are emitted by anything that emits heat. The difference in temperatures between objects provides the contrast to identify between different objects.
Because night vision goggles amplifies available light that bounces off of objects, no light means no amplified image. Since infrared goggles do not rely on ambient light, they do not suffer from the same problem. Objects emit their own infrared light with amounts varying according to how much heat that body has. Infrared goggles can be used in total darkness.
The biggest advantage between the usual night vision and infrared goggles is that the latter is much better at spotting at objects that are partially or totally hidden. A person hidden inside a cardboard box or behind some bushes can be hard to see with the naked eye. With infrared, their heat signature would go through the covering material and be clearly visible to the infrared goggles. How deep the material is depends on how sensitive the unit is.
A bright source of light can overload the device momentarily blinding the person who is wearing the goggles preventing the use of the night vision device. You can stop the use of the infrared device by heating up the area so there is no temperature difference for the device to detect.
I hope this article helps you understand the difference between night vision and thermal imaging.