I'm a newbie too, but this is my understanding. The ? goes in tandem with the :
The line is saying: let's assign a value to $name. The question mark is saying 'is "name" set? If so, assign $_POST['name'] to this variable'. The : is saying 'if not, then assign "" to it'.
EDIT: got distracted by a phone call before clicking Post. Cute Tink's answer is better.