The term contract work breakdown structure refers to the specific portion of he work breakdown structure that has been associated with a specific project that as been developed and is currently being maintained by the seller in is process of attempting to deliver a subproject or project component to the buyer. An example of this would be the subcontracting of a specific activity task within a project to a unique 3rd party whose job it is to complete and deliver that element. The seller, or provider, of that element may create and develop their own individual work breakdown structure which can be both shared with the buyer (as a form of contractual evidence of work to be done) and can also be utilized as a means of planning and organization on an internal level. Contract work breakdown structure can also be referred to by the abbreviation CWBS.
This term is defined in the 3rd edition of the PMBOK but not in the 4th.