If you announce something, you tell people about it publicly or officially.

If you announce a piece of news or an intention, especially something that people may not like, you say it loudly and clearly, so that everyone you are with can hear it.

If an airport or railway employee announces something, they tell the public about it by means of a loudspeaker system.

If a letter, sound, or sign announces something, it informs people about it.

If a meal or a guest is announced by a servant at a formal party, the servant says clearly that the meal is ready or the guest has arrived.