What is diffusion?

All the cells in our body communicate constantly with their surrounding environment in order to feed and excrete their wastes. Various substances in that environment pass through the cell membrane to enter or exit each cell, with the process of diffusion. So basically, diffusion is the movement of something- that being a free moving substance or particle- from a place with a high concentration to a place that has low concentration. For example, oxygen particles in our lungs diffuse from the alveolar air space (the little berry like structures inside the lungs) to the blood vessels and the blood that is circulating around the lungs.