Anybody suggested me, what is web application firewall (WAF)?
A usual firewall protects the client while a web application firewall protects the server. A WAF serves as a reverse-proxy by protecting the server every time the client tries to access it. It protects your website and web applications from defacement, denial of service, data leakage, identity theft and intrusion attempts. It may come in the form of server plugin, filter, appliance or maybe customized to an application.