These boats are generally less expensive to build and have a shallow draft. They can get up on plane easily but unless the water surface is perfectly calm they tend to give a rough ride because of the flat bottom pounding on each wave. They also tend to be less stable and require careful balancing of cargo and crew. Examples of flat bottom boats might be Jon boats, small utility boats, and some high speed runabouts.
It is also used as an adjective, for example: “For more than 50 years, Polar Kraft has manufactured flat bottom utility jon boats and modified V-hull bass-boats that have been extremely popular throughout the Southern US.” IinfK785