Duties - Duties contain privileges. The administrator assigns duties to security roles. A duty can be assigned to more than one role. Both duties and privileges can be assigned to security roles. You can assign related duties to separate roles.
Privilege - A privilege specifies the level of access that is required to perform a job, solve a problem, or complete an assignment. Privileges can be assigned directly to roles. A privilege contains permissions to individual application objects, such as user interface elements and tables.
[View:https://docs.microsoft.com/en-us/dynamics365/unified-operations/dev-itpro/sysadmin/role-based-security:750:50]
See also this video (2 min)
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