An API gateway is a server that acts as an entry point for clients to access various services in a system. It manages requests from users, directing them to the appropriate backend services while handling tasks like authentication, load balancing, and caching. This simplifies the interaction between clients and multiple services, making it easier to manage and scale applications. By using an API gateway, developers can streamline communication and improve security. It allows for centralized monitoring and logging, helping to track performance and troubleshoot issues. Overall, an API gateway enhances the efficiency and reliability of service-oriented architectures.