The movement of molecules from a crowded area (high concentration) to a less crowded area (low concentration) is called diffusion.

Here's a breakdown:

* Diffusion is a passive process, meaning it doesn't require energy input.

* It's driven by the concentration gradient, the difference in concentration between the two areas.

* Molecules move randomly, but overall, there's a net movement from high concentration to low concentration, aiming to reach equilibrium.

Think of it like a drop of food coloring in a glass of water. The dye molecules spread out, moving from the concentrated drop into the less concentrated water until the color is evenly distributed throughout the glass.