Dialyze means to filter or clean
Hemodialysis is a process of filtering the blood to cleanse it of toxic materials.
Diffusion is the process by which waste products are removed from the blood. This process is compared to what happens when you make a cup of tea. Think of the tea bag as a filtering membrane similar to the dialyzer. When you dip the tea bag in the water, the flavoring and color inside the tea leaves pass through the tea bag into the water, but the tea leaves dont pass through. This is because the ingredients causing the color and flavor in the tea on one side of the tea bag passes through to the less concentrated clear water on the other side until the flavor and color are equally distributed. This is how the membrane in the dialyzer works. Large red blood cells do not pass through the membrane, but smaller waste products (BUN, Creatinine) pass through.