Technique that lets several individual efficiently share the same resource.
By this definition trunking can be applied to areas outside of two-way radio even if it mostly used within tele- and radio communications.
How trunking works in practice varies depending on technology. But as an example, in TETRA all radios in the system are placed in a "control channel" when in idle. When a user initiates a transmission the call is automatically assigned an available communication channel. If/when someone answers the conversation will continue on the dedicated channel.
But. if the respons is delayed a pre-defined amount of time all affected radios are placed back on the control channel and if/when the call continues it will be assigned a new available channel.
The images show a conventional and a trunked system in the form of an ordinary cue.