As a noun, spume means the froth you find on sea water. As a verb, it means to make frothy, as in...well...frothy seawater.
If you've ever wondered why seawater produces so much froth, note that the bubbles come from high concentrations of surfactants, or organic material in the water. The spuming, or bubbling action happens when breaking waves introduce air into the water and then trap it in bubble form. To remember spume, just think about the foam that washes up on the beach and sticks there for a time. You could be forgiven for thinking of it as what the ocean spews forth.