Total Internal Reflection is a phenomenon that occurs when a light wave traveling in a denser medium, like water or glass, hits a boundary with a less dense medium, such as air, at an angle greater than a specific critical angle. Instead of passing through, the light is completely reflected back into the denser medium. This effect is crucial in applications like optical fibers, where it allows light to travel long distances with minimal loss. The critical angle depends on the refractive indices of the two media involved. For example, when light moves from water (higher refractive index) to air (lower refractive index), it can only reflect completely if the angle of incidence exceeds this critical angle. Total Internal Reflection is essential in technologies like fiber optics and prisms, enabling efficient light transmission and manipulation.