Refers to a specific type of wave or swell in the sea.
El marullo en la costa era tan fuerte que se podía escuchar desde lejos.
The swell at the coast was so strong that it could be heard from afar.
A medida que el marullo crecía, los barcos comenzaron a balancearse peligrosamente.
As the swell grew, the boats began to sway dangerously.