Your ComPBX is capable of grouping together many extensions into a single dialled extension. For example, if there are sales agents with extensions 220, 221, 222, and 223, then it is possible to assign a 'Sales' ring group which, when dialled, will call all of the phones simultaneously.
Additional options can be configured such as: the ring strategy (ring all, ring sequentially, ring first available, and more), max ring time, announcement (to be played to the caller prior to dialling the group), whether to ring or play music, and more.
This feature is useful for IVR's and call queues as incoming calls can be directed to an entire department with ease. This can also be useful if you wish to contact a group of phones internally (technical support agents, sales, stock control etc.). It is as simple as assigning those phones to a ring group (such as 601), and dialling it from any system phone.