what do the nm or µm for a process technology refer to e.g 22nm process technology for device fabrication
The nanometer number on memory chips generally refers to the smallest "half-pitch" between identical features on the chip, as in this illustration from an IEEE article. 



By this definition, a fairly fine-pitch PCB with 0.004" traces and spaces would be defined as 100 micron (100,000nm). 

On microprocessors, it refers to the "node number" (the smallest feature). A CPU with a 32nm node might have a 50~56nm half-pitch, and a 22nm chip might have a 34nm half-pitch.