Commissioning by the Principal post-handover from the Contractor
This WIKI explains a further step in the process of handover where the Principal makes a building ready for occupation by for example installing chattels and other equipment that will be used in whatever function the building serves.
It also contains a WIKI differentiating between commissioning and testing
The attachment doesn't seem to work, try:
https://www.designingbuildings.co.uk/wiki/Client_commissioning_of_construction_works
It's much the same thing.
Geoff