Hosting is when the domains of a request are not directly associated with the machine's name.
The domains are then called hosted.
web hosting is when a web/http server is provided to you. You don't need to install it yourself or another entity in your company is taking care of it.
The server uses the host headers to serve your code.
A destination email server (mx) can host several domains. It can therefore receive emails from different domains such as:
Because IP v4 addresses are scarce, many hosting providers route: