A wave-piercing boat hull has a very fine bow, with reduced buoyancy in the forward portions.
When a wave is encountered, the lack of buoyancy means the hull pierces through the water rather than riding over the top - resulting in a smoother ride than traditional designs, and in diminished stress on the vessel and crew. It also reduces a boat's wave making resistance.
Design theory calls for very long thin hulls, so in practice most are multi-hulls such as catamarans.
The main current usage areas are passenger ferries and military craft.