Final answer:
Self-diffusion refers to the movement of particles within a substance, while interdiffusion refers to the movement of particles between two different substances.
Step-by-step explanation:
Self-diffusion refers to the movement of particles within a substance, where the particles are all of the same type. For example, if you have a container of water and you add a drop of food coloring, the food coloring molecules will spread out evenly throughout the water.
Interdiffusion, on the other hand, refers to the movement of particles between two different substances. For example, if you have a container with two different gases, such as helium and hydrogen, the molecules of each gas will mix and spread out evenly throughout the container.