A web application firewall (WAF) is a security system designed to protect web applications from various online threats. It monitors and filters incoming traffic to a website, blocking harmful requests while allowing legitimate ones. This helps prevent attacks such as SQL injection, cross-site scripting, and other vulnerabilities that can compromise sensitive data. WAFs can be deployed as hardware, software, or cloud-based solutions, making them flexible for different environments. They analyze HTTP/HTTPS traffic and apply predefined security rules to identify and mitigate potential risks. By doing so, a WAF enhances the overall security posture of web applications and helps maintain user trust.