A web application firewall (WAF) is a security solution designed to protect web applications from various threats such as cross-site scripting (XSS) and SQL injection attacks. By filtering and monitoring HTTP traffic between a web application and the internet, WAFs can identify and block malicious requests while allowing legitimate traffic. These firewalls enhance overall web security by providing an additional layer of protection beyond traditional firewalls. WAFs are essential for maintaining compliance with security standards and ensuring uninterrupted application availability.