This is the 10371st most frequent Turkish word.
birbirlerinin
"Of each other" or "of one another."
In this sentence, 'birbirlerinin' is used to indicate a reciprocal relationship between the friends, where they are mutually involved in the action of glancing.
Arkadaşlar birbirlerinin notlarına göz atıyorlardı.
The friends were glancing at each other's notes.
Here, 'birbirlerinin' refers to reciprocity among the children regarding the toys they were sharing with one another.
Çocuklar, birbirlerinin oyuncaklarını paylaşarak oynuyorlardı.
The children were playing by sharing each other's toys.
In this example, 'birbirlerinin' highlights the mutual respect among the team members toward the ideas of their peers.