This is the 6461st most frequent Russian word.
ярмарку
"Ярмарку" means "fair" or "market fair" in English.
In this sentence, "ярмарку" (fair) is used in the accusative case as the direct object of the verb "посетили" (visited).
Мы посетили ярмарку в центре города.
We visited the fair in the city center.
Here, "ярмарку" (fair) is in the accusative case as the direct object of the verb "проводят" (hold).
Они проводят ярмарку ежегодно в мае.
They hold a fair annually in May.
In this sentence, the word "ярмарке" is used in the prepositional case to indicate the location of the action, governed by the preposition "на" (at).