A variable which is not bound to a specific data type. A variable can contain a string, then assigned an integer, then an array, then an object, etc.
<?php
$var = 'hello';
$var = 100;
$var = array( 1, 2, 'hello', 100 );
$var = new Person();
?>

Seriously?

Yes.

I mean, why this topic?

he's an indian programmer. came here to post links a while back but I deleted the ones where he spammed unrelated threads.