Sea Clouds, also called Ocean Clouds, are large water-like clouds. They form seas in the sky. One can almost sail on it as if it were water except that Sea Clouds are slightly less dense than water, and as such, things that are drop into it will sink faster than in normal water. Another difference of seas made of Sea Clouds from seas made of water is that there is no sea floor. However, they still affect Devil Fruit users like a regular body of water would. These clouds form two known seas: the White Sea and the White White Sea.
Island Clouds are a special type of cloud. They are fluffy, but dense enough to carry all kinds of things. They form islands in the sky seas.
Island Clouds, as well as Sea Clouds, are created when a compound in Seastone called "pyrobloin" is ejected into the air by volcanic eruptions and comes in contact with water vapors. The density of the water vapors determines whether Sea Cloud or Island Cloud will be created. Both these types of clouds are not normally able to survive on the Blue Sea.
Ball Clouds (玉雲,Tamagumo?) are clouds in the shape of balls. Enel briefly uses one as a floating platform when confronting the remaining participants of the Upper Yard Survival.Satori used a variation known as Surprise Clouds (びっくり雲,Bikkurigumo?) in his Ordeal of Balls.