How are the Receiving Office, Elected Office, and Designated Office distinguished in a PCT international application?

It is the office that receives the PCT international application, while a Designated Office is the patent office of a country that the applicant has designated to obtain a patent in. An Elected Office is the patent office of a country selected from among the Designated Offices in order to make use of the preliminary examination results in particular; the Elected Offices may be selected as all or only some of the Designated Offices, and countries not subject to Chapter II of the PCT are excluded.