Security
Firewall
In short and in plain language
A firewall is a filter for data.
It sits between a server and the internet. It lets data through or blocks it by set rules.
A web application firewall also looks at what is in the requests to the site.
It is one part of security. It does not replace updates and upkeep.
Definition
A firewall is a filter that allows or blocks traffic between a server and the internet according to set rules. A web application firewall additionally examines the content of requests to the website. It is one building block of security and does not replace updates and maintenance.