This is the 14536th most frequent Russian word.
партиях
"Партиях" means "in parties" (plural form, prepositional case).
In this sentence, 'партиях' refers to groups organized to promote political ideologies as plural nouns in their prepositional case.
Все говорили о политических партиях страны.
Everyone talked about the country's political parties.
Here, 'партиях' represents gatherings or celebrations, also plural nouns in the prepositional case.
На школьных праздничных партиях было весело.
The school holiday parties were fun.
In this case, 'партиях' denotes musical parts or segments performed by different sections of the orchestra, again plural nouns in the prepositional case.