This is the 14359th most frequent Russian word.
отмену
"Отмену" (accusative form of "отмена") means "cancellation" in English.
The word 'отмену' (cancellation) is used as a noun in the accusative case following the word 'объявили' (announced), explaining the action.
Вчера объявили отмену концерта.
Yesterday, they announced the cancellation of the concert.
Here, 'отмену' (repeal) is a noun in the accusative case used as the direct object of the preposition phrase 'за отмену' (for the repeal).
Мы выступаем за отмену старого закона.
We advocate for the repeal of the old law.
In this sentence, 'отмену' (canceling) is a noun in the accusative case that specifies what was proposed.