What is the meaning of the following work products: WBS task dictionary, documented requests for commitments, and documented commitments?
There are no unique definitions for these terms in the context of the CMMI. Otherwise these terms would be defined in the CMMI Glossary. These are standard Project Management terms.
The WBS Task Dictionary is the list of tasks, deliverables, and predecessor/successor relationships between the tasks. There is sufficient information provided so anyone using the WBS Task Dictionary will have enough information to create a WBS for a project.
Documented Requests for Commitments means exactly what the words say. A request for a commitment. It can be as simple as emailing a document to someone for their commitment and approval.
Documented Commitments again means exactly what the words say. Basically the commitments made by the various parties and stakeholders are written down somewhere.