The Scope Resolution Operator (also called Paamayim Nekudotayim) or in simpler terms, the double colon, is a token that allows access to static, constant, and overridden members or methods of a class.
When referencing these items from outside the class definition, use the name of the class.
Paamayim Nekudotayim would, at first, seem like a strange choice for naming a double-colon. However, while writing the Zend Engine 0.5 (which powers PHP 3), that’s what the Zend team decided to call it. It actually does mean double-colon – in Hebrew! 
class MyClass {
const CONST_VALUE = 'A constant value';
}
echo MyClass::CONST_VALUE;
?>
Two special keywords self and parent are used to access members or methods from inside the class definition. 
Calling a parent’s method
class MyClass
{
protected function myFunc() {
echo "MyClass::myFunc()n";
}
}
class OtherClass extends MyClass
{
// Override parent's definition
public function myFunc()
{
// But still call the parent function
parent::myFunc();
echo "OtherClass::myFunc()n";
}
}
$class = new OtherClass();
$class->myFunc();
?>
