This week's book giveaway is in the Agile and Other Processes forum. We're giving away four copies of Real-World Software Development: A Project-Driven Guide to Fundamentals in Java and have Dr. Raoul-Gabriel Urma & Richard Warburton on-line! See this thread for details.
The links given above should give you a pretty good idea about what a Business Delegate is. From a Struts perspective, the main point of using a Business Delegate is to make this object the link between the Struts Action class and the business tier. An Action class should instantiate and call Business Delegates to get the actual work done. The Action class itself should not contain business logic.