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A transverse magnetic polarization electromagnetic wave bound to an interface through coupling to the material's collective charge response. Its fields propagate along the interface and decay away from it on both sides. In an ideal nonmagnetic lossless planar vacuum-material interface, a real negative relative permittivity below $-1$ supports the bound branch described by the lossless planar surface-plasmon dispersion. Material losses generally make the propagation constant complex.

The energy flux carried into a transmitted wave, integrated over the relevant cross section. The power transmission coefficient compares this with incident power. A displacement or field-amplitude transmission coefficient must be converted with the appropriate wave impedances; its squared modulus alone need not be the power fraction. This distinction applies both to electromagnetic waves and transverse string waves.

A guided electromagnetic wave whose electric field has no component along the propagation axis. Its magnetic field can have a longitudinal component. In an empty perfectly conducting rectangular electromagnetic waveguide, transverse wave numbers determine a nonzero cutoff frequency. This differs from a transverse electromagnetic mode, in which both fields are transverse.

A transverse wave has its oscillating vector perpendicular to the direction of propagation. In a plane electromagnetic wave in vacuum, the electric field and magnetic field are transverse; their orientation is described by polarization of waves.

The upper part of the terrestrial atmosphere includes regions where ionization makes the response to electromagnetic waves depend strongly on mobile electrons. The ionosphere describes that electrical structure; its boundaries need not coincide with the boundaries defined by temperature in the mesosphere and thermosphere.