A federated schema design is a type of GraphQL schema that's designed to be extensible, maintainable, and adaptable to changing requirements. It's built around the concept of a "supergraph," which is a next-generation API gateway capable of encapsulating all the capabilities across multiple products and services. The supergraph is composed of smaller subgraphs, each representing a specific domain or subdomain, and are designed to be independent and reusable. The design principles for a federated schema include thinking in entities, using domain-oriented thinking, making collaboration strategy explicit, and using a subgraph-focused workflow. These principles help ensure that the schema is well-structured, maintainable, and adaptable to changing requirements, allowing developers to build scalable and flexible applications.