General delivery is post addressed to a post office rather than to a door, held at the counter until the addressee collects it in person — General Delivery in the United States and Canada, Poste Restante as the international term, Postlagernd in Germany, Austria and Switzerland, Fermo Posta in Italy, Lista de Correos in Spain.
What Spaw answers
address_type reads general_delivery, and the words that said so land in po_box — GENERAL DELIVERY (Canada's GD is folded onto it, and a station written after it stays: GD STN A reads GENERAL DELIVERY STN A), POSTE RESTANTE, POSTLAGERND — while is_po_box stays false, because a counter is not a rented box. The line stands in for the street, so an address written as general delivery, a town and a postcode is valid without a street; with no street written there is no building to follow into a register, so exists stays null.
The general_delivery risk weight is +40, and unlike the PO box weight it is not waived anywhere. The score measures how far an address is from somebody's own front door, not fraud: a counter is a real delivery point a postal service serves, but nobody can be visited there and a courier cannot leave a parcel at it.
Which spellings are read
The address rules name the general-delivery spellings of 19 countries' postal operators, and in those countries only those are read — Canada's bare GD among them, which counts only at the start of a line, Japan's 郵便局留 and 局留, and Australia's CARE PO. Everywhere else the two international spellings, General Delivery and Poste Restante, are read. A country's page in the address checker lists the words its operator uses.
What it is not
It is not a statement about the person collecting the post. General delivery is a service for anyone who cannot, or would rather not, receive post at a fixed address, and the answer describes the delivery point and nothing else.