In Reverse Osmosis (RO) systems, the water to be purified is pushed against a semipermeable membrane and comes cleaner the other side, the path of water is the reverse of regular osmosis, hence the name. However, it seems to me that this process is pretty similar to a regular filtration.
So, is RO just a fancy term for a fancy filtration? What is it that justifies it not being called filtration, ultrafiltration or some variation of that?