This is the 7785th most frequent Russian word.
институтом
The Russian word "институтом" is the instrumental form of "институт," meaning "institute" or "institution."
In this sentence, "институтом" is instrumental case, indicating the choice or designation of a place for study.
Я поступил в университет, а мой брат выбрал институтом.
I enrolled in a university, and my brother chose the institute.
Here, "институтом" is used in the instrumental case to indicate association with an institution.
Он был с известным институтом связан долгие годы.
He was associated with a famous institute for many years.
In this sentence, "институтом" is used in the instrumental case to show the means or agent through which an action occurs.