PCV Filter - A valve that recirculates gases through the combustion chambers.
Piston rings - A split ring that fits into the groove around the piston. It seals the gap between the piston and the cylinder wall.
Pistons - About the size of a coffee mug, the piston moves up and down in a cylinder like a fist compressing the air/fuel mixture over and over again to be ignited for power.
Plug-in Hybrid - A hybrid electric vehicle that uses rechargeable batteries or an alternative energy storage device that is recharged by plugging it into an external power source.
Powertrain - The path/transfer of power from the engine, to the transmission, to the driving wheels, the connotation of which usually involves warranty coverage of some kind.
PSI - An initialism for 'Pounds per Square Inch', and is usually used measuring air pressure in some way--tire pressure, for example.