A rumble seat is a special seat in a car that is located at the back and faces backwards. It's called a rumble seat because of its bouncy nature like a rumble or vibration.
It's not like our normal car seats that we sit in when we ride in the car. Instead, it's a smaller seat that is usually only big enough for one or two people, smaller than the average car seat.
Back in the old days, when cars were first invented, people used to ride in these rumble seats a lot. It was a fun and exciting way to travel because it allowed the passengers to face backward and feel the wind blowing in their face.
But, nowadays, rumble seats are not very common as they are not considered safe. That's why most modern cars no longer come with them.
So, if you ever see an old car with a rumble seat, you can go ahead and imagine yourself bouncing around in the back, but remember that it's not safe to actually ride in one.