Final answer:
ESB Federation means connecting multiple Enterprise Service Bus systems together to create a unified integration architecture that is scalable and flexible.
Step-by-step explanation:
ESB Federation refers to option b, connecting multiple ESB (Enterprise Service Bus) systems together. This strategy allows an organization to integrate multiple ESB instances that may be spread across different departments or geographical locations, enabling a more scalable and flexible integration architecture. Federation in an ESB context does not solely focus on communication protocols or data formats (which are more related to the internal workings of a single ESB), but rather on the infrastructure that allows different ESB systems to communicate and work as a unified system.