To multiplex is to combine infomation from two or more channels into a single communications channel. Multiplexing is the process of doing this combination. There are various methods available for combining channels of information. These might include: frequency division multiplexing and time division multiplexing, among others.

• Frequency Division Multiplexing
  

  In a broadband network you can combine multiple channels of information by giving each one a different frequency to serve as the base for that channel's information. These different frequencies are then multiplexed into a single broadband channel and sent to a receiver where the various frequencies are demultiplexed into their separate information streams.

• Time Division Multiplexing
  

  In baseband networks digital information is placed directly onto the network cables. Two or more information streams can be combined by interleaving them in a specifically-timed manner. Thus, in time division multiplexing if you looked at the digital data stream you might see, in order, a bit from channel A, a bit from channel B, a bit from... and so on until all of the channels are accounted for when the sequence repeats. At the receiving end a timing pulse is used to determine the start of the sequence and then the bits in the stream are stripped out and each sent to its respective data channel.