A muffler is the part of the car that helps make the engine quieter.
When the engine runs it creates smoke, or exhaust, and that exhaust goes out through the muffler and then the tailpipe.
(from: wikipedia - exhaust system)
Without the muffler the car engine would be very loud.
The word "muffle" actually means to wrap something up to make it quieter,
so just like you can cover your mouth to make sounds quieter the muffler makes a car quieter.
