Yes, HID is headlights. HID = High Intensity Discharge. HID bulbs need a ballast to transform the voltage up REAL high. This high voltage excites the gas in the bulb and creates light. They do not use a filament like a regular halogen bulb. They consume less watts and put out about double the light, very efficient. When you see a car like BMW, Audi, Lexus, etc etc, and there headlights are very bright with a blue tint, thats HID lighting. Its also used to light large outdoor areas, and sometimes indoors, like the parking lot lights at wal-mart.
The K = Kelvin, and is the color temperature. 3000K being a yellowish, similar to regular halogen lights, 6000K is said to be the purest white, and also the brightest of all HID's, 10K is much bluer, but does not give the peak amount of light, there are also green and purple tints, but I dont know the K number of those.
They make a nice upgrade if you do a lot of riding at night. Or you can just get them for the bling factor if you have some money burning a hole in your wallet.
I havent bought any yet. Most sites I find selling them seem kind of sketchy, and often dont list ALL of the specs on the kits they sell, which I tend to shy away from places that seem like their hiding info on the product. I know gixxerfool recently did a write up about installing HIDs and said he got his kit from http://www.cqlight.ca/ I have also found them at sportbiketrackgear.com, they seem like a more reputable site then a lot of the shady sites I have found that seem to ONLY sell HID kits. http://stores.sportbiketrackgear.com/Detail.bok?no=5977
Before you just jump in and buy a kit make sure you find out what bulb size you need for sure. It will depend on what bike you have. And there are diffrent options depending on your head light setup, i.e. diffrent number and sizes of bulbs.