All of these products are models, but they serve different purposes. When people refer to CMMI® V1.3, for example, they could be talking about any of the three CMMI models: CMMI for Development (CMMI-DEV), CMMI for Services (CMMI-SVC), or CMMI for Acquisition (CMMI-ACQ).
CMMI-DEV is used to improve engineering and development processes in an organization that develops products. CMMI-SVC is used to improve management and service delivery processes in an organization that develops, manages, and delivers services. CMMI-SPM (CMMI-ACQ for v1.3) is used to improve supplier management processes in an organization that deals with multiple suppliers for its business.
The People CMM (PCMM) is used to improve workforce management in any organization.
The Data Management Maturity (DMM) model is for the management of an organization’s data assets and corresponding activities.