Diffusion

Diffusion is the movement of a substance from an area of high concentration to an area of low concentration.
Diffusion happens in liquids and gases because their particles move randomly from place to place.
Diffusion also happens in solids through a special type of diffusion called ‘vacancy diffusion’. The diffusion of an atom is therefore dependent upon the presence of a vacancy on an adjacent site, and the rate of diffusion is therefore dependent upon two factors: how easily vacancies can form in the lattice, and how easy it is for an atom to move into a vacancy.
Diffusion is an important process for living things; it is how substances move in and out of cells.