Sean,
Jeremy is right, PD = Pumpe Deuse, a type of diesel fuel injection whereby the fuel is sent to the injectors (the pumpe deuse unit) under low pressure and the injector increases the pressure to injection pressure, very reliable & very economial.
The 115 denotes the power output of your engine in Kilowatts
other terms used are:-
CDI & CRD = common rail diesel, whereby fuel is delivered under high pressure by a single fuel line (the commom rail) to the injectors.
TDi = Turbo Direct injection (not as commonly though, Turbo Diesel injection), injects the fuel directly into the combustion chamber intead of via a "pre combustion chamber"
Kompressor = Supercharger, used to compress & thus increase the volume of air to the engine, more air = more oxygen = more power, advantages, instant responce, disadvantages, bulky uses engine power to drive it.
Turbo = turbocharger, used to compress & thus increase the volume of air to the engine, more air = more oxygen = more power, advantages, uses spent exhaust gasses so no engine power is used to drive it, compact, disadvantages, slower responce.
Both the Galaxy & the Alhambra are made in the same assembly plant in Spain, as is the VW Sharan, they are all derivatives of the same vehicle, but the Seat gives you more for your money.
GeorgeB