This is the 643rd most frequent Indonesian word.
tertentu
Specific.
The word 'tertentu' is used here to describe a specific characteristic of the 'topic', denoting a particular choice or specification.
Saya mencari buku dengan topik tertentu.
I am looking for a book on a specific topic.
In this sentence, 'tertentu' modifies 'waktu', referring to specific times without naming exact instances.
Pada waktu tertentu, jalan ini sangat ramai.
At certain times, this road is very crowded.
Here, 'tertentu' qualifies 'cara', indicating that each person has their own unique or distinct method.