The mode concept of a waveguide containing isotropic medium must be generalized when it is applied to waveguide containing gyromagnetic medium. For ferrite‐ or YIG‐rod waveguides, three families of surface waves are found to exist. They are named as dynamic, surface, and volume modes. Dynamic modes are forward waves. Both surface and volume modes become backward waves when their phase velocities are much smaller than the velocity of light, i.e., large &bgr; values. The transverse‐field vectors are generally elliptically polarized. Therefore, a stationary observer is not able to see the azimuthal and radial variations of a mode. Only by an observer rotating at radian frequency &ohgr;/ncan a constant transverse‐mode pattern be recognized. Using both amplitude and serrodyne‐phase measurements, the differences between the mode concepts of an isotropic rod and a gyromagnetic YIG‐rod waveguide are demonstrated. The same concepts are shown to be applicable to both the gaseous‐ and semiconductor‐plasma waveguides.