This is the 655th most frequent Serbian word.
стадиону
"Стадиону" is the dative or locative case of "стадион," meaning "stadium" in English.
The word 'стадиону' here is used in the dative singular form referring to a location 'at the stadium'.
Ишао сам на велики концерт на стадиону.
I went to a big concert at the stadium.
The word 'стадиону' is again in the dative singular form, indicating the location where the event took place.
На стадиону је одржан важан фудбалски меч.
At the stadium, an important football match was held.
Here, 'стадиону' serves the same function, specifying the vicinity of the location.