This is the 13313th most frequent Russian word.
музыкальном
In English, "музыкальном" means "musical" (prepositional case, singular, masculine/neuter).
Here, 'музыкальном' ('musical') is used as an adjective to describe the type of store, indicating that it is related to music.
В музыкальном магазине можно найти различные инструменты.
In the musical store, one can find various instruments.
In this sentence, 'музыкальном' ('musical') modifies 'конкурсе' ('contest'), emphasizing that the competition was related to music.
Я участвовал в музыкальном конкурсе вчера.
I participated in a musical contest yesterday.
'Музыкальном' ('musical') here describes the type of theater, suggesting performances with music.