Selenium is a chemical element that functions as an essential trace nutrient in biological systems and is utilized in various technological applications. Biochemically, it plays a critical role in the maintenance of redox balance, primarily serving as a cofactor for antioxidant enzymes such as glutathione peroxidase. These enzymatic functions help mitigate oxidative stress by protecting cellular components from damage caused by reactive oxygen species. Outside of biology, selenium compounds are highly valued in material science for their semiconducting properties. This characteristic allows them to be incorporated into advanced electronic devices, making them useful components in photovoltaic cells, photocells, and specialized optical sensors.