A software that listens to incoming web requests (ie: request sent by hitting a button in a browser) from Internet and delegates to the corresponding web application. Conversely it receives outgoing response(s) from the web application and sends it out to the Internet to let it go to the corresponding user.
A web server doesn’t care the content in requests and responses. It only reads the address information so it knows where to send them.
- Mailroom in a company. Workers there receive packages from clients and deliver them to corresponding departments. Conversely they receive packages from departments and send them back to clients. They only care about where to send the packages and don’t care the actual content inside.
- Port control.