Secretion refers to the process in which cells or glands release substances. This biological phenomenon plays a critical role in various physiological functions, from maintaining the body’s homeostasis to communicating with other cells and tissues. The release of substances can be either active or passive, depending on the type of cell or gland involved. Active secretion involves the expenditure of energy by the cell or gland to move substances across membranes, while passive secretion occurs through diffusion or osmosis. The substances that are secreted can range from enzymes and hormones to waste products and toxins, and they serve a multitude of purposes within the body. Overall, secretion is a fundamental process that is essential for the proper functioning of living organisms.