In 1976 the CIE ("Commission Internationale de l'Éclairage", in English "International Commission on Illumination") created an exactly defined color space, the Lab color space. Exactly defined means, that the visual appearance of every color value is defined. Therefore every Lab color value should look the same on every device, if the device is able to display the given Lab value at all. But there is no computer device that can display all Lab values, because the Lab color space is much larger than the RGB and CMYK color space which cover only a part of Lab.
The single components of Lab are L (lightness), a and b. The smaller a is, the more green a color is getting, the larger it is, the more red. The smaller b is, the more bluer a color is getting, the larger it is, the more yellow.