The term for the movement of molecules from an area of higher concentration to an area of lower concentration is called diffusion. This process occurs naturally as molecules spread out to achieve equilibrium in a given space. Diffusion is essential in biological systems, allowing for the transport of nutrients, gases, and waste products across cell membranes. For instance, oxygen diffuses from the bloodstream into cells, while carbon dioxide diffuses out. This passive transport mechanism plays a critical role in cellular respiration and overall metabolism.