Are diffusion and osmosis the same thing?

Diffusion is defined as the movement of a substance from a high concentration to a low concentration, meaning they move from where there are lots of them to where there are fewer. Diffusion of these molecules occurs when the particles are dissolved in water (meaning they are "in solution").

Osmosis means the movement of WATER MOLECULES from a weakly concentrated solution to a strongly concentrated solution; this means the water molecules diffuse from where there are more of them to where there are few.

So you can think of osmosis as a type of diffusion that applies to water! Try to think of the molecules wanting to get from an area where they are concentrated to the area where they are more dilute (there are fewer of them). Remember that both processes occur over a semi-permeable membrane (one that only lets molecules of a certain size through).