First of all, diffusion is generally understood to mean the spreading of particles through random motion from an area of higher concentration to an area of lower concentration. This can be seen, for example, if you put a drop of food coloring into water. At first the drop is mostly together and the color is quite intense, but over time the entire amount of water becomes colored.
Diffusion is seen most often in liquids and air. An example in air is when a bottle of perfume is opened and soon you can smell the scent throughout the room.
In general, diffusion is affected by temperature (the higher the temperature the faster the rate), particle size ( the smaller the particle size the faster it will diffuse), and degree of agitation (stirring or shaking a container of liquid after adding sugar will diffuse the material throughout the liquid faster), and distance (The larger the volume in which the material is placed, the longer it wil take for the material to diffuse throughout)