FDM: Frequency-division multiplexing. A multiplex system for transmitting two or more signals over a common path by using a different frequency band for each signal.

Orthogonal frequency division multiplexing is special case of frequency division multiplexing where a ling serial data streams are divided into parallel data streams and each data stream is multiplied either by orthogonal frequency or code. when multiplied by code known as frequency code division multiplexing and when multiplied by orthogonal frequency then know as orthogonal frequency division multiplexing

Frequency-division multiplexing, wavelength-division multiplexing, and time-division multiplexing.

No, there is no multiplex in the Vatican.

Orthogonal frequency-division multiplexing