WAF
In plain terms
A firewall that filters and blocks malicious web traffic.
Going deeper
A Web Application Firewall inspects HTTP requests to block attacks like SQL injection and XSS before they reach the app. It guards the application layer.
Under the hood
Rule- and signature-based with managed rule sets; complements but doesn't replace secure coding.
Examples
Cloudflare WAF, AWS WAF, blocking SQLi/XSS, OWASP rule sets.
Think of it like...
Like a bouncer screening visitors for weapons before they enter the building.