This is the 846th most frequent Persian word.
جمعی
"جمعی" means "collective" or "group-related" in English.
Here, 'جمعی' is used as an adjective to describe the ceremony as involving or pertaining to a group or a collective nature.
ما در یک مراسم جمعی شرکت کردیم.
We participated in a collective ceremony.
In this sentence, 'جمعی' describes the type of decision-making as being done by or involving a group collectively.
تصمیمگیری جمعی در گروه بسیار مهم است.
Collective decision-making is very important in the group.
'جمعی' here is an adjective describing the space (library) as being shared or used collectively by people.