In a regular radio system (also known as conventional radio), each group of users (like a team or department) is assigned a dedicated frequency. Only one conversation can happen on that frequency at a time, and if the channel is busy, other users have to wait.
However, in a trunked radio system, multiple groups share a pool of frequencies, and the system dynamically assigns an available frequency to users when they need it. This means a more efficient use of frequencies and less waiting for a free channel.