API-first refers to an approach to software development that prioritizes the design and implementation of a well-defined and well-documented API as the foundation of an application, before building the user interface or other application components. This approach is gaining popularity because it enables developers to build more modular, scalable, and flexible applications that can easily integrate with other systems and services. By designing the API first, developers can focus on defining clear boundaries and interfaces for different components of the application, making it easier to develop and maintain the application over time. Additionally, an API-first approach can help reduce development costs and accelerate time-to-market by enabling teams to work in parallel on different aspects of the application.