a term defined by BS 1192:2007 means a spatial subdivision of a project to allow multiple people to work on Project Information Model simultaneously, i.e. Revit.
Volumes illustrate how Project Information Models can be divided into independent units, for a range of purposes.
also two character volume/system field within BS EN ISO 19650-2 Information Container Identification1
1 BS EN ISO 19650-2:2018 National Annex, NA.3.4 p.40