the K stands for Kilo..So its Kilocalories. Just an ancient way of writing it i guess.
As to what is the ideal. Well i Used to think 30% protein, 30% fat and 40% karbohydrates was ideal for bulking. But i found I put on to much fat with that ratio. So ive gone down on the carbs and upped the protein. And it works much better for me. And when i diet down, i just started with removing 15% of the calories from the carbs. Added cardio, removed another 10-15% from the carbs. More cardio. And if i werent where i wanted. Id go down even more on the carbs, but add some more protein. It seems what works for me changes every year. Its not an exact science, but it works.