What characteristic defines a RESTful resource?

A RESTful resource is defined by its identification and addressability through a unique URI (Uniform Resource Identifier). This characteristic is fundamental to RESTful architecture, which emphasizes that every resource should have a unique identifier that clients can use to interact with the resource. By following this principle, clients can easily query, modify, or delete resources using standard HTTP methods (GET, POST, PUT, DELETE, etc.) while ensuring that these resources can be located consistently over the network.

The unique URI not only allows for easy access to resources but also promotes the statelessness aspect of REST. Each request from a client contains all the necessary information needed for the server to fulfill that request, thus eliminating the need for the server to maintain session state for individual clients. This approach helps in scalability and makes the architecture more resilient and flexible.

In contrast, maintaining an application state, lack of addressability, or maintaining ongoing connections with clients does not align with the REST principles. REST is designed to be stateless and resource-centric, which is why the correct characteristic that defines a RESTful resource centers around its identification by a unique URI and its addressability.