An undefined task (also known as abstract task) defines a task for which the type of work is unspecified. This is used to model work done by someone the engine does not need to know of and there is no known system or UI interface. It is also used when modeling a process that is not automated, or while the process automation is in development.
For the engine, an undefined task is handled as a pass-through activity, automatically continuing the process at the moment the process instance arrives.
Undefined tasks have no real benefit for automating processes, and instead provide insights into the tasks that are performed outside of the process engine.
Both Web Modeler and Desktop Modeler default to undefined tasks when adding tasks to your process. You can change the task type by clicking the wrench icon and selecting one of the other types.
An undefined task:
<bpmn:task id="undefined-task" name="Undefined task" />