What is $_GET and $_POST variables? Are they built-in or user-defined variables? Why do we use these arrays?

Ans.  

 The predefined $_GET variable is used to collect values in a form with method="get"

Information sent from a form with the GET method is visible to everyone (it will be displayed in the browser's address bar) and has limits on the amount of information to send.

The predefined $_POST variable is used to collect values from a form sent with method="post".

Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.

All of they are built in variable.

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