This is the 7795th most frequent Russian word.
иркутском
"Iркутском" is the prepositional case form of "Иркутск," meaning "in Irkutsk," referring to the city in Russia.
Here, 'иркутском' is used as an adjective in the prepositional case to describe the theater, indicating its geographical location related to the city of Irkutsk.
Мы побывали в Иркутском драматическом театре.
We visited the Irkutsk Drama Theater.
In this sentence, 'иркутском' functions as an adjective in the prepositional case to specify that the university is situated in Irkutsk.
Он учится в Иркутском университете на биологическом факультете.
He studies at the Irkutsk University in the Biology Faculty.
Here, 'иркутском' is used as an adjective in the prepositional case to denote the location of the zoo in Irkutsk.