When driving out on the highways, a buffer is a car you let drive in front of you so that any police you encounter will stop him and not you.

For example, where I live the speed limit on the highways is 90 km/h (roughly 60 mph). However, my (and many others') preferred speed is in the vicinity of 120 km/h, which leads to rather hefty fines if you get caught. Therefore I usually drive around 105 km/h under normal circumstances. Sometimes I will see a car closing up on me from behind. When this happens I let them pass me, and then speed up and trail them by 100-200 yards. That car is now my buffer. If our mini-convoy now passes a police car that's parked by the side of the road hunting for speeders, the distance is enough for it to get out of hiding and go after the buffer. Should we meet a police car going the opposite way, it will also give you time to slow down.

Finding a suitable buffer can be a very fun game when you're driving, and will often lead to very intense psychological battles between drivers. You see, if your buffer realizes what you are doing, he can slow down and tempt you to pass him. If you do, he will then speed up and use you as his buffer. If you don't pass him at first, it's just a question of who is more stubborn. Personally, I've driven at 80 km/h for close to 20 minutes before the other guy gave up.