In a waveguide or cavity, one of the various possible patterns of propagating or standing electromagnetic fields. Note 1: Each mode is characterized by frequency, polarization, electric field strength, and magnetic field strength. Note 2: The electromagnetic field pattern of a mode depends on the frequency, refractive indices or dielectric constants, and waveguide or cavity geometry. 2. Any electromagnetic field distribution that satisfies Maxwell's equations and the applicable boundary conditions. 3. In data communications, a protocol used to transfer data from switch to switch or from switch to terminal. 4. In statistics, the value associated with the highest peak in a probability density function.