Here's why:
* Common noun: It refers to the general concept of a group of people gathered together for a specific purpose, like a meeting, a gathering, or a conference.
* Collective noun: It refers to a group of individuals considered as a single unit, like a team, a committee, or a parliament.
Therefore, the specific classification depends on the context of its use.
For example:
* "The assembly was held in the auditorium." (Common noun, referring to the general act of gathering)
* "The student assembly voted on the new school policy." (Collective noun, referring to the group of students as a single entity)