What is the difference between osmosis and diffusion?

Simply, is the of water particles whilst the term diffusion is used for any other chemicals/substances.

Diffusion in general refers to the net movement of any particles through a semi - permeable membrane, whilst osmosis involves specifically the movement of water particles through a semi - permeable membrane.

Whilst there are common factors that affect both diffusion and osmosis such as temperature, surface area and concentration gradient; factors such as pressure and affect osmosis specifically.

Hope this helped :)