An optical medium is a material through which light can travel. Common examples include air, water, and glass. The properties of the optical medium, such as its refractive index, determine how light behaves as it passes through, including bending or changing speed. Different optical media are used in various applications, such as in lenses for cameras and fiber optics for telecommunications. Understanding the characteristics of these media is essential for designing devices that manipulate light effectively, enabling technologies like microscopes and telescopes to function properly.