Indirect Reference used in the $$variable.
We explain the difference between $variable and $$variable through below example:-
Suppose, we create two variables.
(1) $variable which has value name.
(2) second variable name is the value of the first variable.
<?php
$variable = "name";
$name="John";
echo $$variable;
?>
Output: John
Work Flow of the above example
$$variable;
$$variable now process will work from right to left.
$name
after that output is
John