Process Task is a task created to work on a specific process. Process usually includes several tasks which can be completed by different team members.
All team members who work on tasks of this specific process have the same goal "to complete the process" and can collaborate and share data during work on this process.
Process Task is always part of the process and has reference to this process.

Process Task can be assigned to a single user (she automatically becomes the assignee as soon as the task is ready to work on). 

Alternatively, Process Task can be assigned to multiple users or groups (candidate assignees). In this case, Process task will be available to all these users as soon as it is ready to work on.

Process task may have access to process data form. Data form shares necessary data between all process tasks according to data form permissions. Data form permissions are configured in a template for each task (i.e. permissions for assignee of the exact task).
Also, this task may use predefined rules for due date calculation.

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