In a people activity, you select or map to an input and an output process variable associated with a task's interface. The input variable contains the data displayed in a user's task client application. For a task, the data is what a user needs in order to complete the task. For a notification, it is the data that informs a user. The input variable copies data from the BPEL process into the task or notification input parts.
The output variable, available only for a task, contains the data the user sends back to the process. The variable copies data to the BPEL process from the task's output parts, which represents the task's result data.