What does PVC and CPC stand for when used in a twin PVC/PVC + CPC cable?

PVC stands for Polyvinyl chloride.


It can be made softer and more flexible by the addition of plasticizers, the most widely-used being phthalates. In this form, it is used in clothing and upholstery, and to make flexible hoses and tubing, flooring, to roofing membranes, and electrical cable insulation.

https://en.wikipedia.org/wiki/Polyvinyl_chloride

CPC is likely Circuit Protective Conductor.

CPC is a system of conductors joining together all exposed conductive parts and connecting them to the main earthing terminal. Strictly speaking, the term includes the earthing conductor as well as the equipotential bonding conductors.

http://www.tlc-direct.co.uk/Book/5.4.2.htm