What are the differences between diffusion and osmosis?

Both these processes involve the movement of molecules from an area of high concentration to low concentration. They are also both passive processes, so happen without the use of chemical energy. However, osmosis specifically refers to the movement of water molecules, whereas diffusion can be any type of molecule. Osmosis also involves a partially or selectively permeable membrane, which means that not all molecules can pass through it. Diffusion can happen anywhere and in both liquids and gases (think of perfume spreading through the air, or squash in water). 

The full definitions are:

Diffusion is the passive movement of particles from an area of high concentration to low concentration.

Osmosis is the passive movement of water molecules from an area of high water concentration to low water concentration, across a partially permeable membrane.