Which process is applied to break down the project into smaller, more manageable elements?

Which process is applied to break down the project into smaller, more manageable elements?
 Scope Definition is incorrect answer according to A Guide to the Project Management Body of Knowledge (PMBOK) published by PMI. At least the 3rd edition of it which I have. But if I recall it right, it has not been changed in the last draft of the 4th edition I saw.
The process is called Create Work Breakdown Structure (WBS) and it is performed to subdivide the major project deliverables and project work into smaller and more manageable components. The output of this processs is the WBS which represents all work that the team has to perform. See Section 5.3 in the 3rd edition.