Propagation constant refers to the rate at which electromagnetic waves travel through a medium. It is also commonly known as the wave propagation constant or the phase constant. Synonyms for the propagation constant include the wavenumber, which describes the spatial frequency of a wave, and the phase velocity, which represents the speed of an individual wave peak. Additionally, the attenuation constant describes the rate at which a wave loses power as it travels through a medium, while the refractive index determines how much a wave bends as it enters a new medium. All these concepts are interconnected and related to the propagation of electromagnetic waves.