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 $$variable; ?>
Work Flow of the above example
$$variable now process will work from right to left.
after that output is