I am looking for an O2 sensor for my 81 Deville. In the part description it includes the phrase "VIN(9)" or other variation of this. What does this mean?

it means the engine size digit is a 9 in your cars VIN (serial) number.

so as long as there is a "9" in my VIN I should be OK?

In the middle of the VIN. Last 6 digits are production number.

Here is my VIN 1G6AD4794B9158511

D479 . Coupe DeVille with a 9 engine.

so I should be GTG then with Bosch 12028 O2 Sensor?

Hey there Haze: The Vin 9 will be the 368 engine. The 80-85 model years will have a 1 wire and a 2 wire oxy sensor. You will most likely need the two wire sensor. They are around $70

does it matter with the V8/6/4 motor?

Does what matter.