K for Kelvin(Colour Temperature)
Yes, photographs also have a temperature aspect to them. They are judged with respect to which part of the spectrum the light might correspond and at what temperature of emission. What it means to me, I got another setting to fiddle with and tweak to my whim. Generally, changing the temperature, makes the photo appear more cooler or warmer. Cooler, being a bluish shade and warmer being the orange-yellowish shade. I use it to calibrate the white balance in my photos mostly. And yeah, shooting in RAW, helps a lot.