PPM stand for parts per million and is a unit used to measure pollutants present in the air.
Power windows have a small motor fitted so as to automate the closing and opening operation. Instead of cranking them by hand it is now done by pressing a button which actuates the motor.
The power to weight ratio of a vehicle refers to how much power it has per kilogram of weight. This is a better indicator of a vehicles performance as a heavier car with more power might be less powerful than a lighter car with lesser power.
Power steering is a system that reduces the effort required to turn the wheels, usually by adding a hydraulic servo cylinder to supply power to the wheels. This can sometimes also be done by electric motors.