In OpenMRS, persons are represented as independent entities. Patients are persons. Clinicians and community health workers are persons. Users of the system are persons. And there are data points that each of these types of persons have - name, birthdate, gender, address, etc.
The purpose of Person Data Definitions is to define these common data points, and to enable them to be retrieved for a particular group of persons that is of interest. This group may be a Cohort of patients, it may be your list of community health workers, it may be your system administrators, etc.
Because all Patients are also Persons, any Person Data Definition may be applied to any patient. But the reverse is not true. Patient Data Definitions may not be appropriate for all Persons. This is why the two constructs are distinct.
TBD - table here containing data definition name, configuration properties, and a description of what each property means