Yes, IR! It means that he body has been prepared for infrared photography in the factory!
On the picture above you see the box. Just because looking at the body as usual, it is not possible to distinguish between standard and IR version. You have to have a look at the bottom of the body – here you would see a red plate on the battery compartment door, saying X-T1 IR. The difference between standard body and the IR version is the filter used just in front of the sensor. In the standard body this is so called hot-mirror – a filter which cuts off both ultraviolet and infrared parts of the light spectrum. In the IR version there is no hot-mirror – all the light reaches the sensor. Without hot-mirror the colors are heavily incorrect. So much, that no white balance system is able to make them correct.
Without the hot-mirror filter there is an addition of both violet, coming from the ultraviolet part of spectrum (UV), what you can see on the sky and red, coming from the infrared part of the spectrum (IR), what you can see on grass and other normally green vegetables, which should be green on the picture because they were green in the field.
OK, removing the hot-mirror effectively destroys the picture. So why to do it? There are two uses: forensics, where UV photography allows for falsification detection and art, where this open a new ways of creativity.
Color photography: IR photography gives us the ability to show the world in quite new colors, like on the picture below:
The above picture I took using the most common IR filter, which cuts off everything with wavelength shorter than 720nm and passes all the rest to the sensor.
Black and white photography: we gain the ability to revere tonal relations between the green objects like grass and trees and the blue sky. We also gain the ability to show dramatic effects of clouds on the sky. And this is my favorite use of IR:
The last picture shows that Lightroom isn’t the best to convert X-T1 IR RAW to black and white – or I haven’t discovered the correct way yet 🙂