Diffusion is the movement of particles (atoms, ions, molecules) from a region in which they are at a higher concentration to regions of lower concentration.
A good example of diffusion is food coloring. If a drop of blue food coloring is placed in a beaker of water, eventually the entire beaker of water will have a blue tint. The particles of food coloring move through the water until they are equally distributed throughout the beaker.
Diffusion takes place along a concentration gradient. A concentration gradient exists until the diffused substance is evenly distributed.
