Light propagation refers to the way light travels through different mediums, such as air, water, or glass. It moves in straight lines in a vacuum, but its path can bend or change speed when it enters a new medium. This bending of light is known as refraction, which is why objects may appear distorted when viewed through water. The speed of light is approximately 299,792 kilometers per second in a vacuum, but it slows down in denser materials. This change in speed can also lead to phenomena like total internal reflection, which is utilized in fiber optics to transmit data efficiently over long distances.