Colors are assigned values on a scale of 0 to 255. Red Green Blue all have values between 0 through 255. When you want pure blue, set blue values to 255, and green and red values to 0. Or to get a pure white, set red green and blue to 255 and you will have a perfect white. S is saturation or the strength of color and it's a percentage of the color minus the amount of gray.
B is for brightness which is relative tone or the lightness of a particular color.
It's also measured in percentages. CIE Lab defines a color spectrum that is broader than any of the other models. CIE Lab color is designed to be device-independent, meaning that common colors actually look alike, regardless of the device that is displaying it. These files seem to be rather large and the not commonly used.