Gerund functioning as a noun meaning ‘the act or process of separating’.
separatinggerund / present participle More accurate classification: present participle functioning adjectivally.
The separating wall between the two rooms was very thin.
Разделяющая стена между двумя комнатами была очень тонкой.
The separating factor in their decision was the cost.
Отделяющим фактором в их решении была стоимость.