Contrary to popular belief.
Unless you're into dumpster diving, waste is not really a fun concept to think about for the vast majority of the population. Of course that's only because the vast majority of the population isn't made up of gearheads because to us, exhaust systems are a fascinating world of their own. Especially when it regards making a car either more powerful or louder. The only problem is that like many things in life, there are many misconceptions about the exhaust system. Especially when it comes to back pressure.
Put simply, back pressure is pressure headed back into the exhaust and takes place when the pressure of the surrounding atmosphere is greater than that of the exhaust. Simple logic will tell you that excessive back pressure will hinder the exhaust system's performance by impending on the exhaust flow.
That means lost horsepower (imagine trying to breathe quickly while sprinting and having a hard time exhaling). The problem is that regulating optimal amounts of back pressure is not easy. Install a restrictive exhaust and back pressure is increased, though such systems also have the effect of increasing the velocity of the exhaust, On the other hand a wider exhaust will reduce back pressure but slow the flow of exhaust gas, meaning it can't escape into the atmosphere as fast. As always, Jason Fenske of Engineering Explained takes the time to explain these concepts in terms we can all understand so that you can school your less enlightened gearhead friends.