Difference between $message and $$message

eg1

$message = "ume";
$ume = "All Interview dot com";
echo $message; // Output: ume
echo $$message; // Output: All Interview dot com


eg2
$Message = "YOU";
$you= "Me";
echo $message //Output:- you
echo $$message //output :-Me

It means
$message is a variable and
$$Message is variable of variable

A variable of variable allows us to change the name of
variable dinamically