This is the 5635th most frequent Turkish word.
partilerinin
"Partilerinin" means "of their parties" in English.
The word 'partilerinin' in this sentence functions as possessive, indicating 'of the parties'.
Bu yıl birçok siyasi partilerinin liderleri bir araya geldi.
This year, many leaders of political parties have come together.
Here, 'partilerinin' denotes possession related to 'their parties'.
Partilerinin görüşlerini her zaman dikkatle dinlerim.
I always listen attentively to their parties' opinions.
In this usage, 'partilerinin' indicates the possessive form signifying 'of the parties of various groups'.