PC = Process Coated
PU = Process Uncoated
SM = Solid Matte
SU = Solid Uncoated
MC = Metallic Coated and so on
fyi... copied/pasted from above link
The following designations for PANTONE Colors used in earlier versions of PANTONE COLOR BRIDGE are now obsolete:
PC = process simulation, coated paper, i.e., PANTONE 185 PC.
UP= uncoated paper, process simulation, i.e., PANTONE 185 UP.
EC - Euro process simulation, coated paper, i.e., PANTONE 185 EC. This was used in the European version which is now obsolete.