PCS

From ColorWiki

Profile Connection Space

The Profile Connection Space is the color space - either Lab or XYZ - where two ICC device profiles connect together.

ICC device profiles convert from device space (RGB, CMYK, etc) to the PCS and back again. The advantage of this architecture is that color transformations between two devices can be built 'on-the-fly'. The CMM simply concatenates the two profiles into a color transformation and then converts colors through it.