The surf zone extends from where waves begin interacting with the bottom (~1.3 times wave height in depth) to the shoreline. Waves break differently depending on bottom slope: spilling (gentle), plunging (moderate, best for surfing), surging (steep).
It is a high-energy zone where rip currents, longshore drift, and most beach drownings occur. Width depends on wave conditions and bathymetry, varying from metres on steep beaches to hundreds of metres on gently sloping ones.