Sometimes I see this code in php :
$car = & new Car();
instead of
$car = new Car();
What's the meaning of the ampersand sign?
The & assigns by reference -- that is, if you say $a =& $b;, then $a and $b refer to the exact same thing, and changing one will change the other.
Its use with new like this, is mostly a leftover from PHP4 -- back then, PHP used to copy objects when assigning them, and that could cause big problems when you are doing stuff like DOM manipulation. It's rarely (i think never) required with objects in PHP5 (since now object variables are references anyway), and i think it's even considered deprecated.