They represent atomic units of work done as part of a business process. 

There are three types of tasks:

• None: represents a generic task. This type of activity does not have an associated application; it is automatically executed by the engine and affects neither the relevant workflow data nor the application data.
• Script: are those activities that do not require interaction by the user and will be executed by the Workflow engine.
• User: represents a task executed by a user.

Below are examples of each one of these symbols: