What does multiplexing mean (in it's abstract form)? I understand you have 'multiplexers' in hardware and 'muxing' in networks. What would a good high-level definition be?
Since the definition is basically 'the doing of multiple things at the same time' or 'interleaving of many things'. I would suggest it's as simple as that when applied to computer science.
Though are are specific instances of multiplexers such as putting multiple signals through a data channel, other words in computer science may also be used to replace multiplexer. For example you could consider the running of many processes as multiplexing but the more common term is multiprocessing.
However the hardware/software example of many signals over a wire/channel is the canonical example for me.
There's a nice definition here - .../wiki/multiplex.