CMMC is primarily designed to protect Federal Contract Information (FCI) and Controlled Unclassified Information (CUI).
FCI is information, not intended for public release, that is provided by or generated for the government under a contract to develop or deliver a product or service to the government, but not including information provided by the government to the public (such as on public websites) or simple transactional information, such as necessary to process payments.
CUI is generally unclassified information that requires safeguarding or dissemination controls pursuant to and consistent with law, regulations, and government-wide policies. A CUI Registry provides information on the specific categories and subcategories of information that the Executive branch protects. The CUI Registry can be found at both https://www.archives.gov/cui and https://www.dodcui.mil/Home/DOD-CUI-Registry/