What does osmosis refer to?

Osmosis specifically refers to the movement of water molecules through a selectively permeable membrane. This process is driven by the concentration gradient of water on either side of the membrane. Water will naturally move from an area of lower solute concentration (where there is a higher concentration of water) to an area of higher solute concentration (where there is a lower concentration of water), in an effort to achieve equilibrium. This is a vital process for maintaining cellular functions and is crucial in many biological systems.

The focus on water is what distinguishes osmosis from other forms of diffusion. While diffusion can encompass the movement of air or solutes, osmosis is strictly concerned with water and its ability to traverse membranes selectively impenetrable to certain solutes. The movement of water against a concentration gradient does not define osmosis, as this process generally relies on the natural flow along the gradient rather than opposing it.