WAF aka web application firewall is a web application firewall that helps protect your web applications from common web exploits that could affect application availability, compromise security, or consume excessive resources. A WAF’s primary responsibility is to stop bad traffic from entering your network. This could be bots that are generating a lot of fake traffic or state-sponsored attacks from a country that is on a blacklist. A WAF allows you to determine what types of traffic you will allow, including geographical regions or the type of device that is generating traffic. This gives you as an operator a multitude of options to secure the network as well as ensure compliance.
in other words
The MOAT around your App.