Diffusion is the driving force that facilitates the movement of molecules from a region of higher concentration to a region of lower concentration. This movement occurs as a result of random molecular motion, and it is driven by the tendency of molecules to spread out and occupy the available space.

Diffusion is a passive process, meaning that it does not require any input of energy. It occurs spontaneously as a result of the thermal energy of the molecules. The rate of diffusion is proportional to the concentration gradient, which is the difference in concentration between two regions. The greater the concentration gradient, the faster the rate of diffusion.

Diffusion is essential for many biological processes, such as the transport of nutrients into cells and the removal of waste products. It also plays a role in the movement of water and other molecules across membranes.