The phenomenon that occurs when light travels through a prism is called refraction. When light enters a prism, it changes speed due to the difference in density between air and the prism material. This change in speed causes the light to bend, separating it into its different wavelengths or colors, typically forming a spectrum. This effect explains why we see the colors of the rainbow when white light passes through a prism, demonstrating fundamental principles of optics and the nature of light.