This is the 740th most frequent Hebrew word.
חברתי
"Social" or "Societal".
In this sentence 'חברתית' is used as an adjective to describe the activity as 'social', referring to its nature as an interaction among people.
הפעילות החברתית בבית הספר מחברת בין התלמידים.
The social activity at the school connects the students.
Here, 'חברתי' is an adjective that describes the research as 'social', indicating its focus on societal aspects.
יש לי עניין רב במחקר חברתי על שינויי תרבות.
I am very interested in social research on cultural changes.
'חברתי' in this context modifies 'service', defining it as oriented towards society and community involvement.