Dollar /

$ is character, used in various situations:

• As the first character of a variable

• As an operator, for variable variables.

When associated, PHP and $ often leads to the conversion rate of dollars to Philipini Pesos.

<?php

$a = 'b';
$b = 'c';

echo $$a; // 'c'

echo $\{$a}; // C

?>

Documentation

See also Why Does PHP Use the $ Sign for Variables? and Programming archaeology: PHP’s dollar sigil.

Related : Interpolation, Variables, Variable Variables, Relaxed Keywords, Single Quotes Strings