Respuesta :

grangergirl
A whitecap is a wave that is breaking– it is characterized by the white water/foam on the top of the wave. 
A swell is a slow, rolling wave that does not have the white water on top. Swells tend to be larger. 
Hope that helps!
Ezi
A swell is a slow rolling wave and a white cap is a frothy kinda wave. :)