This is the 911th most frequent Turkish word.
partisinin
"Partisinin" means "of his/her/its party" or "of their party" in English.
Here, 'partisinin' indicates possession and is used to specify that it is Ayşe's party.
Ayşe, partisinin başarısını kutlamak için bir etkinlik düzenledi.
Ayşe organized an event to celebrate her party's success.
In this sentence, 'partisinin' (derived to 'arkadaşlarının partisini') refers to the party belonging to his friends.
Ali, arkadaşlarının partisini çok beğendi.
Ali really enjoyed his friends' party.
Here, 'partisinin' implies the possession of the programs by the political leader's party, indicating affiliation.