WAF
A reverse-proxy filter that blocks common web exploits before they reach the origin server.
Definition
A Web Application Firewall inspects HTTP traffic and blocks requests matching known-bad patterns: SQL injection, XSS, path traversal, credential stuffing. Cloudflare, AWS WAF, and Fastly all bundle WAF capability. Application owners tune rule sets and exception lists. A WAF is not a substitute for secure code but raises the cost of automated probing.