noun, verbal noun, の adjective
A place where people meet and do deliberation. Sounds boring, but also sounds like some kind of meeting or conference.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
I started getting hungry during the assembly.
You ditched the conference to watch a serial TV drama!? What the heck!?
The purpose of this meeting is to discuss our current situation and go over new plans.