What does PCD mean?
PCD stands for (pitch circle diameter), this is the diameter of a circle drawn through the center of your wheel's bolt holes. PCD is measured in millimetres and also indicates the number of studs or bolts the wheel will have. The most common fitment has 4 studs with a PCD of 100mm, hence the fitment 4x100. Check the fitment guide above to check the fitment of your car, if you are unsure consult a technician.
What does OFFSET (et) mean?
Your car requires a unique offset. This is where the wheel will sit in relation to the bodyline of the vehicle, realistically you can go 5-7mm outside these recommendations, but always consult a technician if you are unsure, as there are often other factors that need to be considered. Offset is usually stamped on the wheel and is measured in millimetres of et (et is the short form of the German word 'Einpresstiefe' which literally translates as insertion depth).
taken from
http://www.alloywheels.com/fitmentguide.aspOh and does anyone know what "ET" is ( other than Estimated Time , Phone Home Alien Types )