What is diffusion? Diffusion is a process of removing the sharp gradients. Over time, the process of diffusion creates entropy, it takes a system from the state of order to the state of disorder. But why?
Here is a simple animation of what diffusion means in physics.
Here is an example of how we can simulate a simple diffusion proces using particles.
The two examples may look different, but the first process describes the evolution of the diffusion process. While if we want to write down the profile instead of the particles themselves, the picture corresponds to the second one.