What does the K mean in the White Balance (WB) mean on my Nikon D90 camera?

I have a Nikon D90 in the WB section where you choose the settings, tungsten, florescent cloudy, sunny. And then i get to "K" for what settings would i use this function?

According to Ken Rockwell: " This setting lets you choose any amount of blue or orange. Once you select "k" you choose the value, from 2.500 to 10.000 with the front knob while you hold WB… 2, 500k is very, very blue,… 3, 200k is the same as the tungsten,… 5, 400k is the same as the direct sun,… 10, 000k is very, very orange"
I believe it is like a manual setting in contrast with the others which are presets.

The K stands for Kelvin. As in the temperature scale: http://en.wikipedia.org/...iki/Kelvin