What is the difference between WSGI, CGI, and FastCGI in web application development?

In web application development, WSGI, CGI, and FastCGI are different middleware protocols that help connect web servers with web applications.

1. **WSGI (Web Server Gateway Interface):**
WSGI is a standard interface between web servers and web applications in Python. It provides a common interface that allows for interoperability between different web servers and application frameworks. WSGI is typically used with Python-based web applications like Flask and Django.

2. **CGI (Common Gateway Interface):**
CGI is one of the oldest methods for connecting web servers with web applications. It works by spawning a new process for each incoming request, which can be inefficient for high-traffic websites. CGI scripts can be written in various languages like Perl, Python, and PHP.

3. **FastCGI:**
FastCGI is an improvement over CGI that aims to reduce the overhead of spawning new processes for each request. Instead of creating a new process for each request, FastCGI uses a pool of persistent processes to handle incoming requests, making it more efficient for high-traffic websites. FastCGI is often used with web servers like nginx and Apache.

In summary, while WSGI is specific to Python applications and provides a common interface for interoperability, CGI is a more traditional but less efficient method for connecting web servers with web applications. FastCGI improves upon CGI by using persistent processes for handling requests, making it more efficient for high-traffic websites.