According to the BACnet protocol documentation:

Defines a standardized object whose properties represent a collection of other objects and one or more of their properties. A group object is used to simplify the exchange of information between BACnet devices by providing a shorthand way to specify all members of the group at once. A group may be formed using any combination of object types.

Objects of type group have the following properties:

•description

•listOfGroupMembers

•objectIdentifier

•objectName

•objectType

•presentValue

•profileLocation

•profileName

•propertyList

•tags