A workflow instance interacts with several SharePoint objects (task lists, and documents or items) during its lifetime. In SharePoint, you can have many workflow instances running at the same time and interacting with several objects at the same time. To be able to identify which workflow instance is interacting with which object, you must use an identifier that links one particular workflow instance to one particular SharePoint object. Each workflow instance must be bound to its own items. Such an identifier is called a Correlation Token. A correlation token links a workflow instance to its documents, items, and tasks. It prevents confusion between different workflow instances. We need have one correlation token for the workflow and one for each task we create during the workflow, so that when a user completes a task we have a unique identifier with which to receive any input from the user into the workflow. Make sure correlation token names are not repeated in different task.