SERVER_NAME: This predefined variable tells us the name of the server hosting the webpage.
REQUEST_METHOD: This predefined variable tells us which HTTP request method was used to access the page, such as GET or POST.
Predefined variables are special variables that PHP automatically makes available to programmers. We do not have to create these variables ourselves. They can provide useful information about the server, user request, files, forms, sessions, cookies, and other parts of a website while a PHP script is running.