This is the 2375th most frequent Russian word.
объявлена
"Объявлена" means "declared" or "announced" in English.
The word 'объявлена' is used in passive voice to indicate that an announcement was officially made by someone.
Эпидемия была официально объявлена властью.
The epidemic was officially declared by the authorities.
Here, 'объявлена' describes that a specific event (session) has been announced or made known to the participants.
Объявлена сессия вопросов и ответов после лекции.
A question-and-answer session was announced after the lecture.
In this instance, 'объявлена' denotes that a declaration regarding the state of emergency has been made, referring to an official notification or enactment.