What is a RESTful API?

A RESTful API is an application programming interface that adheres to the principles of Representational State Transfer (REST), which is an architectural style for designing networked applications. REST is based on a set of conventions and best practices that allow for interaction with web services in a stateless manner, using standard HTTP methods such as GET, POST, PUT, and DELETE.

The key characteristics of a RESTful API include stateless communication, where each request from a client contains all the information needed to process that request, and the use of resource-based URLs that represent the entities being manipulated. This design allows for easy scalability and interoperability between different systems, making RESTful APIs popular for web services.

In contrast, the other options do not accurately describe what a RESTful API is. A protocol for real-time applications refers to specific communication methods for instantaneous data transfer and is not specific to REST. Syntax for writing web code implies a focus on programming languages or markup, which does not encompass the principles of RESTful architecture. Similarly, a database management system pertains to the management of databases, rather than the creation of networked applications and communication protocols. Thus, the definition of a RESTful API as one that follows the principles of REST is the most accurate.