A Web Application Firewall (WAF) is primarily responsible for filtering and monitoring HTTP/S traffic to and from a web application. It is designed to protect web applications by filtering and monitoring traffic for malicious requests, such as SQL injection, cross-site scripting (XSS), and other common application-layer attacks. A WAF helps secure web applications by analyzing the HTTP/S traffic and blocking any harmful requests before they reach the application.

Anti-virus Software is used to detect and remove malicious software on endpoints and devices but is not designed to filter HTTP/S traffic specifically for web applications. Load Balancer is used to distribute network traffic across multiple servers to ensure performance and reliability, but it does not focus on security filtering. Intrusion Detection System (IDS) monitors network traffic for suspicious activity but operates at a different level of the network stack and is not focused solely on web application traffic.