In simple terms, "flat bottom" refers to something that doesn't have a rounded or curved surface at the bottom. It means that the bottom area is straight and even, like a tabletop or a stable base.
Sentences with «flat bottom»
The leather wrapped flat bottom steering wheel is a joy to hold and steer. (autosarena.com)
They are simply square, open boxes with flat bottoms and raised sides. (dogs.lovetoknow.com)
The main instrument connecting the driver to the road is the steering wheel and this unit features a thick rim as well as flat bottom. (topspeed.com)