FastCGI is a protocol that allows web servers to communicate with applications more efficiently than traditional CGI (Common Gateway Interface). It enables web applications to run persistently, meaning they stay in memory and can handle multiple requests without restarting, which improves performance and reduces latency. By using FastCGI, developers can create dynamic web content that responds quickly to user requests. This protocol supports various programming languages, making it versatile for different web development environments. Overall, FastCGI enhances the speed and scalability of web applications, making it a popular choice among developers.