What is the difference between net diffusion and diffusion?
The diffusion is a random process from a region of higher concentration to lower concentration down the concentration gradient
Let's say you have a membrane which can allow water movement but not sugar molecules. At the very beginning the water particle will move towards the less concentration area, but as time passes some particles move from sugar's area to where the water originally came from. Net Diffusion is a net movement (where the maximum particles moved) movement of particles from a region of higher concentration to lower concentration down the concentration gradient