Any car exceeding the speed limit, whose speed you match with your car while maintaining a reasonable distance behind them. The idea is that the "Guinea Pig" will get caught in any Speed Trap up ahead, and you'll have time to react, slow down, and continue on your way.
I always look for a "Guinea Pig" when I have to drive through the city. It makes it so much easier to make good timing safely.
This term is used when you notice that a woman has under gone breast augmentation with implants. Artificial breasts. Usually the term is used when they are blatantly obvious. Reebok - "The pump" Reebok was the first tennis shoe that used a pump to increase the conformability of the shoe. "Pump it up"
When you visit California, you will notice alot of Reebok, particularly in the Los Angeles area.