Final answer:
Osmosis is the net diffusion of water through a semipermeable membrane down its concentration gradient, usually toward a higher solute concentration facilitated by aquaporins.
Step-by-step explanation:
The term that refers to the net diffusion of water down its concentration gradient through a selectively permeable membrane is osmosis. Osmosis involves water movement through a semipermeable membrane to balance the concentration of solutes on both sides. When a membrane is permeable to water but not to solutes, water will diffuse toward the side with a higher solute concentration, thus resulting in a net flow of water across the membrane. Aquaporins play a significant role in facilitating this movement of water, especially in red blood cells and kidney tubules.