"Trunk" denotes a connection to another network, e.g. the public telephone network. A connection to another network can be e.g. an "ISDN trunk", a connection to the Internet an "SIP trunk". Connections (trunks) of the same type can be combined to form groups. The trunks of a trunk group then have the same properties - the trunk groups can therefore be seen primarily as capacity expansions.

Different trunk groups can be differently prioritized by the administrator. The result is e.g. that calls are handled with preference given to a cost-efficient connection (e.g. an SIP trunk directly to the Internet). If this is not available, a lower-priority path is selected, e.g. an ISDN trunk to the normal telephone network, see help.enreach.com/cpe/13.28/Administration/Swyx/en-US/index.html#context/help/Trunks_TrunkGroups_$.