Multiplexing lets several information streams share one physical communication resource by assigning them distinguishable portions of that resource.

In time-division multiplexing (TDM), users or streams take turns in separate time slots. The receiver uses timing information to separate the interleaved symbols or samples.

In frequency-division multiplexing (FDM), different streams occupy different frequency bands at the same time. Frequency-selective filters separate the bands at the receiver.

Guard time or guard frequency may be left between allocations to tolerate imperfect synchronization and non-ideal filtering.

TDM and FDM are physical or signal-level multiplexing strategies. They are distinct from packet switching, where independently addressed packets from many flows are statistically interleaved by a network.

The common principle is resource separation: transmissions are arranged so the receiver has a distinct time or frequency allocation by which to tell them apart.