Diffusion is the movement of molecules from a region of high concentration to a region of low concentration. This movement occurs due to the random motion of molecules, and it continues until the concentration of the molecules is equal throughout the system.

Here's a breakdown of the key points:

* High concentration: The area where the molecules are more densely packed.

* Low concentration: The area where the molecules are less densely packed.

* Random motion: Molecules are constantly in motion, bumping into each other and changing direction.

* Net movement: The overall movement of molecules is from high to low concentration, even though individual molecules move randomly.

Diffusion is a fundamental process in many biological systems, including:

* Cellular transport: Nutrients and oxygen move into cells, while waste products move out.

* Gas exchange: Oxygen diffuses from the lungs into the bloodstream, while carbon dioxide diffuses from the bloodstream into the lungs.

* Signal transduction: Chemical messengers diffuse across synapses to transmit signals between neurons.