Port 443 is the default port used by Hypertext Transfer Protocol Secure (HTTPS) for secure web communications. HTTPS is the encrypted version of HTTP, which is utilized to secure transactions and to ensure privacy and data integrity. When a web server is configured to use SSL or TLS, it will listen on port 443 for secure connections. The other ports mentioned are used for different protocols or purposes: For example, port 80 is the standard port for HTTP, which is not encrypted, while port 110 is used by POP3 for email reception, and port 21/22 are used for FTP/SSH respectively.