An Analogue Repeater can only handle one voice traffic channel at any instant. EG only one person can transmit over the repeater, other users have to wait until the repeater becomes free.
With medium and large sized radio systems quite often one or more user groups may want to talk at the same time. To enable this a Trunked Repeater system is required.
With a Trunked system there will be two or more repeater channels available. On pressing the Transmit button the radio will automatically transmit only on a free channel.
Trunking can be configured on Digital and Analogue radio systems although certain Digital repeaters now come with two channel trunking as standard.