What are the differences and similarities between osmosis, active transport and diffusion?

Osmosis is a term used to describe the movement of water molecules from a high water potential to a low water potential. Diffusion is similar to this, however it is used to describe the movement of molecules, other than water, from high concentration to low concentration. Both of these processes are passive, meaning they do not use energy. These therefore contrast with the process of active transport, which uses energy in the form of ATP. This process involves the movement of molecules from a low concentration to a high concentration, across a cell membrane.