the day when the British Queen or King's birthday is officially celebrated, especially with the ceremony of TROOPING THE COLOUR in London. It is not the same as the Queen or King's own personal birthday, and it is always on the second Saturday of June.
a UK law by which people who work for the government are not allowed to discuss their work with people who do not work for the government or to make known information which should be kept secret. Government workers must 'sign the Official Secrets Act' (= agree to obey this law), and they can be put in prison if they break this agreement.