This is the 4083rd most frequent Russian word.
одесса
"Одесса" is the Russian name for the city of Odesa, a port city in southern Ukraine on the Black Sea.
Here, 'Одессу' refers to the city 'Odessa' in the accusative case as the object of the sentence.
Я собираюсь посетить Одессу этим летом.
I'm going to visit Odessa this summer.
In this sentence, 'Одесса' is the subject and refers to the city as the entity being described.
Одесса славится красивыми пляжами.
Odessa is famous for its beautiful beaches.
'Одессой' is in the instrumental case here, used in the prepositional phrase indicating location in relation to the noun.