Movement of a substance from an area of higher concentration to one where it is less concentrated in

Diffusion is the movement of solutes from a higher concentration to a lower concentration.

It is important not to confuse this with osmosis, which refers to the movement of water only (from a lower concentration solution to a higher concentration solution.)

Diffusion and osmosis almost always goes hand-in-hand. A good way to remember this is if you imagine mixing a powdered juice drink. Diffusion talks about the powder's movement while osmosis talks about the water's movement.

They formed the oceans.  as they melted water was formed and the water made the oceans