Its a object pointer.
$FOOD->getfood("cookie");
Would call the function getcookie from the object FOOD, and do the functions operations.
In the object you can set variables.
var foodtype;
in many cases you want to use this variable in a few or all of your functions. So to make the variable transportable between them you use a pointer aswell, but this pointed doesnt call from a object.
example:
function getfood($food) {
$this->foodtype = $food;
}
You should look more into it..