What is the significance of using ".php?id=15" in PHP files and how is it related to variable passing?

Using ".php?id=15" in PHP files allows for passing a variable (in this case, "id") through the URL. This is commonly used to retrieve specific data or perform actions based on the value of the passed variable. To access the value of "id" in the PHP file, you can use the $_GET superglobal array.

$id = $_GET['id'];
// Now $id contains the value passed through the URL